Journal Mobile

Author Affiliations: 
Correspondence to: 

Arkiath Veettil Raveendran, Badr Al Samaa, Barka, Sultanate of Oman  Email:

Journal Issue: 
Volume 49: Issue 3: 2019
Cite paper as: 
J R Coll Physicians Edinb 2019; 49: 207–16



Sepsis is a major cause of death in hospitalised patients accounting for mortality rates as high as 60% and, hence, is called ‘a hidden public health disaster’. Sepsis is defined as life-threatening organ dysfunction caused by a dysregulated host response to infection. Sepsis is not a disease but is a clinical syndrome, where the initial features are nonspecific resulting in delayed diagnosis. Lack of specific laboratory tests to diagnose the syndrome adds to the diagnostic confusion. Failure to identify sepsis in the early stages itself delays effective treatment resulting in high morbidity and mortality. Various biomarkers and newer laboratory tests help to address these issues. However, to date there is no ideal test to diagnose sepsis. The most commonly used markers are C-reactive protein (CRP) and procalcitonin (PCT). There are around 180 biomarkers reported to be useful in sepsis. In addition to CRP and PCT, various emerging laboratory markers, such as like serum amyloid A, soluble triggering receptor expressed on myeloid cell-1, mannan and antimannan antibodies, and interferon γ inducible protein-10 etc., have been reviewed and their clinical usefulness discussed in this paper.

HTML Full Text


Sepsis is one of the most common causes of death in hospitalised patients and, hence, it is called ‘a hidden public health disaster’. Sepsis is associated with mortality rates as high as 60%.1

Risk of sepsis is increasing worldwide posing challenges to the medical fraternity. The factors contributing to increased incidence of sepsis include advanced age, performance of more invasive procedures, associated multiple comorbidities and emergence of antibiotic resistance.2

Sepsis was initially defined as a clinical condition associated with infection and at least two of the four criteria for systemic inflammatory response syndrome (SIRS), which are: 1) temperature >38°C or <36°C; 2) tachycardia; 3) tachypnea; or, 4) white blood cell count >12,000 or <4,000. Sepsis is not a disease but is a clinical syndrome.3 Because of inadequate specificity and sensitivity the recent sepsis (Sepsis-3) guidelines recommend avoiding use of SIRS criteria and proposed a new definition: a life-threatening organ dysfunction caused by a dysregulated host response to infection.4 A new measure, qSOFA [quick sequential (sepsis-related) organ failure assessment], was introduced, incorporating altered mentation, systolic blood pressure of ≤100 mmHg and respiratory rate of ≥22 breathes per minute, which are quick bedside clinical tools for identifying adult patients with signs of infection who are likely to have poor prognosis.5

Even though there are various guidelines, international discussions and published algorithms to assist early diagnosis and treatment of sepsis, diagnostic confusion still persists resulting in improper (under or over) treatment. Infectious Diseases Society of America had multiple disagreements with the 2016 Surviving Sepsis Campaign’s recommendations published under the auspices of the Society of Critical Care Medicine and the European Society of Intensive Care Medicine.6

Early diagnosis and assessment of severity are important essential steps for early comprehensive treatment, thus reducing sepsis-related morbidity and mortality. An ideal biomarker should be validated, inexpensive and widely accessible, and results should be rapidly available. There is no ideal test to diagnose sepsis and various biomarkers are helpful to make a reasonable conclusion in the context of clinical scenario. As per Pierrakos and Vincent,7 around 180 biomarkers are reported to be useful in sepsis and the figure is likely to increase in the future. However, only a few biomarkers are assessed as appropriate for the diagnosis of sepsis. Lack of proper assay methods and interference with the testing methods limit the use of various biomarkers in clinical practice. The most commonly used and widely available markers are C-reactive protein (CRP) and procalcitonin (PCT). Other emerging useful markers are serum amyloid A (SAA), soluble triggering receptor expressed on myeloid cell-1 (sTREM-1), mannan (Mn) and antimannan (A-Mn) antibodies, and interferon gamma inducible protein-10 (IP-10).

Biomarkers can be used in suspected sepsis for 1) identifying or ruling out sepsis; 2) evaluating the severity and assessing the prognosis; and, 3) evaluating patients’ response to proper treatment.

Diagnosis of sepsis mainly relies on demonstration of presence of organism by blood culture. The time required for the culture to become positive and insensitivity of culture under various situations limits its use as an early diagnostic modality in patients with suspected sepsis.8 In order to overcome the limitations of culture to diagnose microbial infections alternative molecular-based methods such as enzyme-linked immunosorbent assay kits, flow cytometry, immunoluminometric assays, polymerase chain reaction (PCR) tests, automated microbiological systems and fluorescence in situ hybridisation techniques are used.7

Biomarkers in sepsis

A biomarker has been defined as ‘an indicator of normal biological processes, pathogenic processes or pharmacologic responses to a therapeutic intervention’. Doherty et al.9 defined a biomarker as ‘a characteristic that is objectively measured and evaluated as an indicator of normal biologic processes [or] pathogenic processes’. The most commonly used biomarkers of sepsis include CRP, PCT, SAA, Mn and A-Mn, and IP-10. There are lot more markers in the pipeline. There is no single ideal biomarker so multiple biomarkers are used in concert to achieve better results.

The clinical relevance of a biomarker depends upon its diagnostic accuracy. A biomarker becomes more relevant as its sensitivity, specificity, positive-predictive value and negative-predictive value increases. Positive and negative likelihood ratios also predict the strength of a biomarker as a diagnostic test.10

Why we need biomarkers in sepsis

Sepsis is a critical illness with high mortality, but the initial features are nonspecific and the diagnosis is based on nonspecific physiological criteria (syndromic approach), which results in delayed diagnosis.

Lack of specific laboratory tests to diagnose and high percentage of negative microbiological tests even in patients with sepsis add to the diagnostic confusion. Underestimation of disease severity in the early stage delays effective treatment resulting in high mortality in patients with sepsis. In order to overcome these limitations medical researchers are in continuous search for better laboratory tests and the search for ideal biomarkers still continues.

Pathophysiology of sepsis

Sepsis is a dysregulated host response to infection and involves generalised inflammatory response away from the site of infection or injury. Usually the balance between proinflammatory and anti-inflammatory mediators regulates the inflammatory process. Sepsis occurs when this balance is lost and more proinflammatory mediators are released, causing generalised response exceeding the boundaries of local tissue injury. The multifactorial causes for this response include direct effect of microorganisms and their toxic products, release of large quantities of proinflammatory mediators and compliment activation. Multiple molecules involved in these complex processes are identified and proposed as biomarkers that can be used as indicators of sepsis.11,12

Depending upon the pathophysiological stages of sepsis, biomarkers can be grouped into different categories. The classification of laboratory markers based on pathophysiological stages of sepsis is given in Table 1.

Table 1 Classification of laboratory tests based on the pathophysiological stages of sepsis

Laboratory tests


Proinflammatory cytokines

TNF-α, IL-1β, IL-6, IL-8, MCP-1

Elevated level of IL-6 in people with sepsis is associated with increased mortality and also predicts the benefit of treatment.71

IL-8 helps in the diagnosis of sepsis, whereas MCP-1 helps in the prediction of mortality72,73


Biomarkers of complement proteins


In severe sepsis C5a levels are very high74

Biomarkers of activated neutrophils and monocytes

CD64, integrin CD11b, TREM-1, HBP (azurocidin), soluble form of RAGE, CD14

TREM-1 has a higher predictive power for poor survival in ED patients than do PCT or CRP. 13

HBP is a good predictor of severe oedema and vascular collapse in patients with severe sepsis.14

RAGE is able to predict survival in severe sepsis and CAP. 15

CD14 is high in patients with bacterial infection and its levels correlate with the severity of sepsis16

Biomarkers related to infectious organisms and their products

HMGB1, calgranulins and myeloid-related proteins

Released from damaged neutrophils during inflammation. Are high in patients with sepsis17

Biomarkers of the immunosuppressive phase of sepsis/anti-inflammatory markers

Monocyte HLA-DR expression, CTLA-4 in T cells, PD-1 in monocytes and T cells, CD28 in T cells, IL-10, TGF-α

Low levels of HLA-DR expression predict the development of sepsis, poor survival and increased risk of hospital-acquired infection.19

Increased expression of CTLA-4 and PD-1 are also seen in patients with sepsis.

Decreased expression of CD28 is seen in sepsis.

IL-10, TGF-α levels are high in sepsis

Biomarkers of organ dysfunction

Renal function test, liver function test, serum lactate, lactate clearance, angiopoietins, soluble adhesion molecules, endocan, syndecan-1, heparin sulphate

Syndecan-1 and heparin sulphate indicate injury to endothelial glycocalyx, which is the antiadhesive and anticoagulant surface of endothelium

Pathophysiological basis of biomarker assay

Sepsis results from exaggerated immune response to infection. Various inflammatory agents and products released during the inflammatory process can be potentially useful biomarkers in sepsis. At the later stage of sepsis patients develop compensatory anti-inflammatory response syndrome (CARS) during which various anti-inflammatory mediators will be useful as biomarkers. Products from the infecting organism will help to identify and plan treatment in sepsis. Patients with sepsis may develop dysfunction of various organs, which are also reflected by various markers.

Proinflammatory cytokines

Proinflammatory cytokines are markers of the hyperinflammatory phase of sepsis. These are tumour necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6, IL-8 and monocyte chemoattractant protein 1 (MCP-1). They are the important inflammatory cytokines with prognostic value in sepsis.

PCT and CRP as biomarkers of sepsis

PCT and CRP are common proteins synthesised in response to infection/inflammation and are useful as biomarkers in patients with sepsis.

Biomarkers of activated neutrophils and monocytes

Activation of neutrophils and monocytes in sepsis results in increased expression of CD64 and integrin CD11b, which can be potentially useful to diagnose sepsis.

Triggering receptors expressed on myeloid cells-1 (TREM-1), heparin-binding protein (azurocidin) released from polymorphonuclear leucocyte (PMN) granules and CD14, which helps the monocyte and macrophage to recognise endotoxin, are useful markers in sepsis.13–16

Monocyte activation markers, such as soluble form of the receptor for advanced glycation end products (RAGE), are able to predict survival in severe sepsis and community-acquired pneumonia.15 Since lung alveolar type 1 cells normally express high RAGE levels, soluble RAGE is found to be high in patients with pulmonary infection even in the absence of sepsis.

Biomarkers of infectious organisms and their products

Blood and other body fluid culture is the gold standard for confirming bacterial infection. Use of automated monitoring systems like VITEK® (bioMérieux, USA), ESP Culture System (Trek Diagnostics Inc., USA), BacT/Alert® (bioMérieux) and BACTEC™ (BD, USA) increases the speed and efficiency of blood culture. Use of molecular diagnostic technologies, such as bacterial DNA fragments by real-time PCR in blood samples, or 16S rRNA fragments of Gram-positive and Gram-negative bacteria and 18s rRNA of Candida, might be helpful for early identification of the infectious pathology. Identification of bacteraemia by amplifying specific target nucleic acid sequences using PCR identified double the number of positive specimens compared to conventional blood culture in surgical intensive care unit (ICU) setup in patients with severe sepsis. A high level of endotoxin is a significant risk factor for the development of sepsis. High-mobility-group box 1 (HMGB1), calgranulins and myeloid-related proteins are released from damaged neutrophils during inflammation.17 Currently, 16S rRNA and 18S rRNA gene sequencing are the best methods to identify microorganisms. Matrix-assisted laser desorption ionisation-time of flight mass spectrometry is a novel method that helps to identify the microorganisms quickly and accurately.18 Microarrays that help in large-scale screening for simultaneous diagnosis and detection of many pathogens are also increasingly used for microbial detection. Gene resistance detection testing, loop-mediated isothermal amplification assay and metagenomic assay are other microbial detection methods used in clinical microbiology.18

Biomarkers of the immunosuppressive phase of sepsis/anti-inflammatory markers

With the reorganisation of CARS the role of anti-inflammatory markers in sepsis attracted attention and it was found that monocyte human leucocyte antigen–DR isotype (HLA-DR) expression will improve after initial suppression in survivors of sepsis, usually within 10 days.19

Biomarkers of organ dysfunction

Deranged renal and liver function tests indicate renal and hepatic dysfunction. Serum lactate is one of the common markers used to assess organ dysfunction. Since liver plays an important role in lactate clearance its level can be elevated in patients with liver dysfunction as a part of organ failure in sepsis. Systemic inflammation induces increased anaerobic glycolysis resulting in elevation of blood lactate level in sepsis. Mitochondrial dysfunction associated with sepsis also contributes to increased lactate level. Serum lactate level >2 mmol/l is regarded as a sensitive marker of septic shock. Decreasing or normalised lactate levels indicate recovery from septic shock.20 Serum lactate >4 mmol/l with a systolic blood pressure of at least 90 mmHg is defined as ‘cryptic shock’.21 In critically ill patients the mortality risk rises with increase in serum lactate levels. In one study serum lactate level >4.0 mmol/l was associated with a 27% mortality rate compared to those with lactate level between 2.5 and 4.0 mmol/l where the mortality rate was 7%.22 Low lactate clearance is useful as a predictor of mortality in patients with sepsis.23 Serial measurement of serum lactate will help to assess the disease progression in patients with sepsis.23 At least 10% lactate clearance at 2 hours of initiation of resuscitation is a positive sign of response to resuscitation in patients with severe sepsis.24

Endothelial dysfunction in sepsis contributes to organ dysfunction and markers of endothelial activation, such as angiopoietins, soluble adhesion molecules and endocan, were found to be high in patients with sepsis.

Involvement of coagulation system also adversely affects the clinical course of sepsis. Presence of disseminated intravascular coagulation (DIC) increases the risk of mortality in patients with sepsis.

Microparticles are vesicles shed from the cell surface by blebbing. Microparticles release their contents that have an important role in systemic inflammation and DIC in patients with sepsis.25

Clinically relevant biomarkers in sepsis

There are large numbers of biomarkers in the pipeline. The following are clinically relevant biomarkers that have been found to be useful in patients with sepsis (Table 2).

Table 2 Biomarkers and laboratory tests useful in the management of sepsis



Current status in clinical practice


Acute phase reactant produced by liver in response to inflammation or tissue damage

Commonly used.

Low specificity as sepsis biomarker


Prohormone of calcitonin. Produced in response to infection

Commonly used.

Correlates with severity of infection.

Helps to discriminate infectious and noninfectious systemic inflammation.

Useful as diagnostic test and as prognostic marker as is a marker of severity of sepsis and associated mortality.

Helps to assess the response to treatment

ChT activity

Secreted by activated macrophages

Needs evaluation


Produced in response to bacterial infection

Reflects the severity of infection.

Promising biomarker for early diagnosis and potentially superior to PCT for predicting prognosis in patients with sepsis45


Produced by antigen-presenting cells in response to microbial products and inflammatory stimulus

High specificity and positive-predictive value for bacterial infection in critically ill paediatric patients46


Produced from the liver.

Synthesis is induced by IL-6, which is produced in response to inflammation

Reliable marker of both early and late-onset neonatal sepsis47


An apolipoprotein.

Major acute-phase protein

Equivalent to or more sensitive than CRP


Produced in response to microbial products, hypoxia and proliferative signals

Increased in septic shock.

Helps to differentiate survivors from nonsurvivors49


Acute phase reactants

id="x.3135">Not an impressive marker50

Pentraxin 3

Binds to specific pattern of fungi, bacteria and virus inducing phagocytosis. Secreted by various cells, such as leucocytes and endothelial cells

Correlates with sepsis severity and sepsis-associated coagulation/fibrinolytic dysfunction.75,76

In patients with febrile neutropenia after chemotherapy high pentraxin 3 values predict the development of septic shock and bacteraemia


IL-6, IL-8, TNF-α and IL-1 receptor antagonist

Immune-modulating agent that is produced from nucleated cells

Correlates with sepsis severity and outcome


Released by activated macrophage

Not a predictor of in-hospital mortality in patients with sepsis

Proteins C

Coagulation biomarkers

Low levels in neutropenic patients predict severe sepsis and septic shock

BPW analysis

Based on activated partial thromboplastin time

For diagnosis of sepsis



Member of immunoglobulin super family. Expression upregulated in presence of bacteria or fungi

Superior to CRP and PCT as an indicator of sepsis.57

Indicates the severity of sepsis



Expressed in various cells.

Takes part in various immunological functions

Less useful in sepsis

Midregional pro-adrenomedullin

Potent vasodilating and bactericidal agent

Good predictor of severity and outcome of CAP59

Polymorphonuclear CD64 index

Upregulation of CD64 expression is an early immune response to bacterial infection

Early detection of sepsis in neonates60

Mean neutrophil volume

Volume, conductivity and scatter parameters of neutrophils are a useful tool to identify bacterial infection

Very accurate and sensitive method compared to the manual method of identifying bacterial infection61

Mannan and antimannan antibodies

Mannan is present in the cell wall of invasive fungal organisms

Diagnostic marker of sepsis that is due to fungal infection62


Proinflammatory cytokine

Useful as a biomarker for diagnosing viral infections63


CRP is an acute phase protein that belongs to the pentraxin family of calcium-dependent ligand-binding plasma proteins, produced by liver in response to inflammation or tissue damage. Various cytokines induce its production. However, IL-6 is its prototypical stimulus. Serum levels of CRP increase 1,000 fold during inflammation. CRP level begins to increase within 4–6 hours after the stimulus and doubles every 8 hours. Its half life is 19 hours and the peak level attained at 36–50 hours. CRP is widely used as a marker of infection and sepsis. Various studies have shown the CRP cut-off value to diagnose infection is between 5 and 10 mg/dl.26 The role of CRP as a diagnostic predictor was analysed in various studies and one study showed that CRP had a sensitivity of 84.3%, specificity of 46.15%, positive-predictive value of 84% and negative-predictive value of 42.8%.27 However, measurement of CRP after the onset of sepsis failed to predict the chance of survival in comparison with PCT and IL-6.28 The major drawback of CRP as a sepsis biomarker is its low specificity. CRP has high negative-predictive value to exclude sepsis, if measured in the early course of illness.29 CRP levels >100 mg/l are usually due to bacterial infection, whereas levels <100 mg/l are due to fungal infection, thereby helping to differentiate among the two.30

CRP levels are also increased in various rheumatologic conditions, inflammatory bowel disease, haematological disease and graft-vs-host disease. CRP is also used to assess the inflammation associated with atherosclerotic cardiovascular disease.


PCT is a prohormone of calcitonin. In healthy individuals PCT is produced from parafollicular cells of the thyroid and neuroendocrine cells of the lung and intestine. However, in patients with bacterial infection PCT is produced from numerous organs in the body. PCT is classified as a ‘hormokine’ in view of its relation with both the hormone calcitonin and the inflammatory cascade. Normal reference value of PCT is ≤0.15 ng/ml. Localised infections (without systemic signs) usually show a level between 0.15 and 2.0 ng/ml. PCT level >2.0 ng/ml is usually associated with systemic bacterial infection/sepsis or severe localised bacterial infection. PCT levels increase within 2–4 hours of infection and the maximum level is reached by 6–8 hours and with continued infection or sepsis the elevated level persists.31 Once infection is controlled PCT levels halve daily. PCT half-life is about 20–24 hours. PCT levels persists as long as the inflammatory process continues and the level correlates with the severity of sepsis. PCT is produced in response to endotoxins or inflammatory mediators released in response to bacterial infection.

PCT levels correlate with the severity of infection and help to discriminate patients with infectious and noninfectious systemic inflammation, differentiate bacterial from viral and fungal infections and help to identify bacterial superinfection in patients with viral infection. Studies showed that higher PCT on the day of admission to ICU is associated with increased risk of progression to severe sepsis and septic shock.32 In an observational study it was found that sepsis diagnosis based on PCT level is more reliable than clinical diagnosis.33 In critically ill patients the high maximum PCT level and a PCT increase for 1 day are independent predictors of 90-day mortality.34 PCT values help in deciding about the need for antibiotics and duration of antibiotic therapy.35 It was also found that use of PCT helps in reduction of antibiotic prescription between 11% and 74%, and reduction of days of antibiotic therapy by between 13% and 55%.36 In patients admitted to ICU use of PCT-based algorithm resulted in the reduction of antibiotic therapy for the initial infection by 2 days and the total duration of antibiotic therapy by 4 days.37 In patients with community-acquired pneumonia it is a useful marker to guide antibiotic therapy. In patients with sepsis a 30% decrease in PCT levels between days 2 and 3 is an indirect indicator of effective antibiotic therapy and associated with better survival than CRP levels. Serial measurement of PCT in sepsis can guide antibiotic therapy and helps in therapeutic decision-making.38 Analysis of cost effectiveness of the use of PCT-based algorithm shows that it reduces the length of hospitalisation, antibiotic therapy and number of blood cultures.39 The MOSES study showed that inability to reduce PCT levels by more than 80% between baseline and day 4 is a significant independent predictor of increased 28-day all-cause mortality.40 PCT kinetics have prognostic implications in patients with sepsis.41 PCT level-based treatment results in reduction in the duration of therapy and mortality in critically ill patients.42

Studies have shown that PCT can be used as a diagnostic test and as a prognostic marker, to assess the response to treatment, as well as a marker of severity of sepsis and associated mortality.

Various studies have shown that PCT is superior to CRP in the identification and assessment of severity of sepsis.43 PCT has been found to be more sensitive and specific for bacterial infection than CRP. However, the superiority is not clearly demonstrated in patients with sepsis.44 PCT is useful in predicting the results of blood culture in patients with critical illness. PCT fails to differentiate sepsis from SIRS; however, low levels of PCT are helpful in ruling out sepsis because of their high negative-predictive value. PCT levels rise earlier than those of CRP helping in early anticipation of diagnosis of sepsis 24–48 hours before the CRP levels would.

PCT can be falsely negative in people with localised infection, infection with atypical bacteria and in patients on steroids. PCT levels can be increased in patients with severe trauma, having surgery or after cardiac arrest.

Plasma chitotriosidase triode activity

Chitotriosidase triode is synthesised and secreted by specifically activated macrophages and belongs to the mammalian chitinase family. Chitotriosidase triode is increased in various disorders in which macrophages are activated, such as Gaucher’s disease, atherosclerosis, malaria and haematological disorders.


Presepsin is a 13 kDa protein present in CD14. CD14 is the receptor for lipopolysaccharide–lipopolysaccharide-binding protein (LPS–LBP) complex. In the presence of infectious agents CD14 activates toll-like receptor-4, leading to proinflammatory cascades resulting in the shedding of LPS–LBP–CD14 complex, and plasma protease then generates a soluble CD14 subtype called presepsin. Its production is induced by bacterial phagocytosis and it is the body’s response to bacterial infection.45


IL-27 levels are useful for identifying bacterial infection in critically ill paediatric patients.46 Their overall predictive power improves when used in combination with PCT.


Hepcidin is a peptide hormone produced by the liver that has an important role in iron metabolism. Hepcidin interferes with microorganisms’ access to iron. It is a reliable marker of both early and late-onset neonatal sepsis.47


SAA is an apolipoprotein whose levels increase 1,000 times by 8–24 hours after the onset of infection.

Macrophage migration inhibitory factor

Macrophage migration inhibitory factor (MIF) is a pleotropic immune regulatory cytokine that promotes the migration and recruitment of leucocytes into the site of inflammation and infection. MIF is produced from immune cells (monocyte/macrophage, B and T cells) as well as endocrine, endothelial and epithelial cells.48 When used in combination with other biomarkers MIF has greater value. MIF is a regulator of innate immunity, which is increased in septic shock, and helps to differentiate survivors from nonsurvivors.49 High levels of MIF and PCT in patients with severe burns is associated with a lethal outcome.

LPS-binding protein

LPS-binding protein is an acute phase reactant. It binds to LPSs of Gram-negative bacteria to form LPS–LBP complex, which in turn binds to CD14 and toll-like receptors to induce signal transduction, leading to the activation of the mitogen-activated protein kinase and nuclear factor κB pathway.50

Pentraxin 3

Pentraxins are a super family of proteins that act as pattern recognition receptors and are involved in the acute immunological response. There are two types: 1) classic ‘short’ pentraxin, which includes serum amyloid P component and CRP; and, 2) long pentraxin 3 that binds to specific patterns of fungi, bacteria and viruses inducing phagocytosis. However, pentraxin 3 is also found to be elevated in noninfectious inflammatory conditions limiting its role.


Cytokines are immune-modulating agents that are produced from nucleated cells. In patients with septic shock there are increased levels of both proinflammatory and anti-inflammatory cytokines, and cytokines have been proposed as a biomarker in neonatal and adult sepsis. High and/or increasing levels are associated with poor prognosis; however, studies show that cytokines (IL-6, IL 8) are less useful than PCT and CRP in sepsis.51 IL-6, IL-8, TNF-α and IL-1 receptor antagonist (IL-1ra) levels show correlation with sepsis severity and outcome. Increased levels of IL-6 and IL-8 in neonates predict early onset sepsis. In children with septic shock serum IL-8 levels within 24 hours of admission had 95% negative-predictive value for mortality;52 however, IL-8 is a poor marker in adults with septic shock. Low IL-8 is associated with the high negative-predictive value for sepsis.

IL-6 and IL-8 levels are altered in various conditions, such as major surgery, trauma, exacerbation of autoimmune disease, transplant rejection and viral infections. IL-10, which plays a role in CARS, is found to increase in patients with septic shock and help to predict mortality at 28 days.53 Use of combined cytokine scores using IL-6, IL-8 and IL-10 are a better predictor of mortality than PCT and CRP.

In a study conducted with 17 different cytokines, nine (IL-1, IL-2, IL-4, IL-6, IL-8, IL-10, interferon γ, granulocyte-colony stimulating factor and MCP-1) were able to differentiate survivors from nonsurvivors in sepsis, whereas the remaining eight (TNF, IL-5, IL-7, IL-12, IL-13, IL-17, macrophage inflammatory protein-1 and granulocyte-macrophage colony-stimulating factor) cytokines were not different in both groups.54 Persistently elevated IL-6 is associated with multiple organ failure and death in patients with sepsis.


HMGB1 is a 30 kDa nuclear and cytosolic protein mediating local and systemic inflammation. In comparison to TNF-α and IL-1B it reacts more slowly and, therefore, has been evaluated as a prognostic marker; however, it did not predict in-hospital mortality in patients with sepsis.55

Coagulation biomarkers

As a part of sepsis patients develop various haematological problems including DIC.

Biphasic waveform analysis

Biphasic waveform analysis is based on activated partial thromboplastin time and has been found to be useful for the diagnosis of sepsis.56

Soluble receptors


TREM-1 is a member of immunoglobulin super family. Its expression is upregulated in the presence of bacteria or fungi resulting in release of sTREM-1.57

Soluble form of urokinase type plasminogen activator

Soluble form of urokinase type plasminogen activator is expressed in various cells, such as neutrophils, lymphocytes, monocytes, macrophages, endothelial cells and tumour cells, which take part in various immunological functions. High levels of the soluble form of urokinase type plasminogen activator (suPAR) are associated with increased mortality in patients with HIV, tuberculosis, malaria and Crimean-Congo haemorrhagic fever.58

Midregional pro-adrenomedullin

Serum adrenomedullin (ADM) is a potent vasodilating and bactericidal agent that is found to be elevated in sepsis. ADM is rapidly broken down in the circulation, therefore, the midregional fragment of pro-ADM, is measured.59

Polymorphonuclear CD64 index

Circulating PMN cells bind to endothelial cells and express CD64 during an inflammatory response. CD64 is a high affinity FC receptor for IgG and upregulation of CD64 expression is an early immune response to bacterial infection.60 Other surface markers, such as CD14, CD18, CD25 and CD28, help to predict mortality at 28 days.

Mean neutrophil volume

Sepsis is known to produce numerical and morphological changes in leucocytes. The volume, conductivity and scatter parameters of neutrophils are useful tools even in the absence of elevated white cell count to identify bacterial infection. The change in the morphology and in the number of these cells, which is reflected in the volume, conductivity and scatter parameters of leucocytes, proves to be a more accurate and sensitive method than the manual method.61

Biomarkers for fungal infection

Mn and A-Mn antibodies

Mn is present in the cell wall of invasive fungal organisms. In patients with invasive fungal infection, such as candidiasis or aspergillosis, Mn and A-Mn antibody levels are elevated making it as a useful diagnostic marker of sepsis due to fungal infection. A study showed that a combination of Mn and A-Mn provides better results than either marker alone.62 β-D-glucan test, which is highly sensitive and specific for invasive mycosis, is usually performed along with Mn and A-Mn antibody testing.

Biomarkers for viral infections


IP-10 is a proinflammatory cytokine that is potentially useful as a biomarker for diagnosing viral infections.63 IP-10 has also been found to be useful in guiding treatment in patients with hepatitis C infection.

Traditional markers, such as neutrophil count and CRP, are unable to differentiate infection from inflammatory response. The sensitivity and specificity of CRP for the diagnosis of sepsis is 0.75 and 0.67, respectively, whereas for PCT they are 0.77 and 0.79 and for sTREM-1 they are 0.79 and 0.8, respectively.64–66 Differentiating infectious causes from noninfectious causes of inflammation still remains a challenge.

The receiver–operator characteristic (ROC) curve for various biomarkers helps to assess their discriminative power. The shape and area under the curve (AUC) help to find out the clinical usefulness of a marker. An ideal discriminating biomarker has an AUC of 1, but for a nondiscriminating marker AUC is 0.50. The AUCs for detection of a bacterial cause of inflammation were 0.50 for suPAR, 0.61 for sTREM-1, 0.63 for MIF, 0.72 for PCT, 0.74 for neutrophil count, 0.81 for CRP, 0.84 for the composite three-marker (neutrophil count, CRP, PCT) test, and 0.88 for the composite six-marker test.67 Another meta-analysis showed that AUC for the seven biomarkers, PCT, CRP, IL-6, soluble triggering receptor expressed on myeloid cells-1, presepsin, LBP and CD64 were 0.85, 0.77, 0.79, 0.85, 0.88, 0.71 and 0.96, respectively.68

Infections are the common cause of clinical deterioration in patients with systemic lupus erythematous and antineutrophil cytoplasmic antibody-associated vasculitis. However, clinical deterioration has to be differentiated from disease flare because immunosuppressives are the mainstay of treatment in active disease. If the clinical deterioration was due to infection, inadvertent treatment with immunosuppressive agents results in further deterioration of the patient. So differentiation of infective causes from disease flare is important. However, the commonly used laboratory tests are of limited use in these aspects. It was shown that CD64 expression on neutrophils helps to differentiate bacterial infection from the flare of autoimmune diseases with a sensitivity and specificity of 85% and 84%, respectively, whereas PCT differentiates with a sensitivity and specificity of 75% and 85%, respectively.69 sTREM-1 levels are not found to be useful in this aspect.69

Panel of biomarkers

To date there is no single ideal biomarker for the diagnosis of sepsis hence a combination of biomarkers are used to provide better results. Combinations of multiple markers are expected to increase the sensitivity and specificity in diagnosis and prognosis of patients with sepsis. ‘Bioscore’, which consists of sTREM-1, PCT and PMN CD64 index, has been found to be more useful.70 The probability of diagnosis of sepsis increases with an increase in biomarker positivity, with 3.8% when the bioscore is 0 (i.e. all the markers are below threshold) to 100% when the bioscore is 3 (i.e. all the three markers are above threshold).70 A combination of PCT and biphasic waveform also increases the specificity for the diagnosis of sepsis compared to either marker alone. Measurement of another combination of biomarkers, such as suPAR, sTREM-1 and MIF along with CRP, PCT and neutrophil count, was also found to be more useful than individual agents in patients with SIRS to detect community-acquired bacterial infections with an AUC (ROC-AUC) of 0.88.67


Sepsis is a critical illness associated with exaggerated systemic inflammatory response to infection resulting in high morbidity and mortality in patients admitted in ICUs. Early diagnosis and prompt action improves the prognosis. Lack of specific clinical features delays the diagnosis. Various biomarkers are available to help the clinician to diagnose, plan the treatment, assess response to treatment and to predict the outcome. Even though many potential biomarkers have been evaluated CRP and PCT still remain the most commonly used and widely available biomarkers in sepsis. However, to date, there is no single ideal biomarker for sepsis and hence a combination of biomarkers are used along with clinical characteristics of the patient to provide early diagnosis and better risk assessment. ‘Bioscore’, which consists of sTREM-1, PCT, PMN CD-64 index and a combination of biomarkers such as suPAR, sTREM-1 and MIF, along with CRP, PCT and neutrophil count are found to be more useful in this aspect.


1 Kauss IAM, Grion CMC, Cardoso LTQ et al. The epidemiology of sepsis in a Brazilian teaching hospital. Brazilian J Infect Dis 2010; 14: 264–70.

2 Coelho FR, Martins JO. Diagnostic methods in sepsis: the need of speed. Rev Assoc Med Bras 2012; 58: 498–504.

3 Vincent JL, Opal SM, Marshall JC et al. Sepsis definitions: time for change. Lancet 2013; 381: 774–5.

4 Singer M, Deutschman CS, Seymour CW et al. The Third International Consensus Definitions for Sepsis and Septic Shock (Sepsis-3). JAMA 2016; 315: 801–10.

5 Vincent JL, de Mendonça A, Cantraine F et al. Working Group on “Sepsis-Related Problems” of the European Society of Intensive Care Medicine. Use of the SOFA score to assess the incidence of organ dysfunction/failure in intensive care units: results of a multicenter, prospective study. Crit Care Med 1998; 26: 1793–800.

6 IDSA Sepsis Task Force. Infectious Diseases Society of America (IDSA) Position Statement: Why IDSA Did Not Endorse the Surviving Sepsis Campaign Guidelines. Clin Infect Dis 2018; 66: 1631–5.

7 Pierrakos C, Vincent JL. Sepsis biomarkers: a review. Crit Care 2010; 14: R15.

8 Chan T, Gu F. Early diagnosis of sepsis using serum biomarkers. Expert Rev Mol Diagn 2011; 11: 487–96.

9 Doherty M, Wallis RS, Zumla A; WHO-Tropical Disease Research/European Commission joint expert consultation group. Biomarkers for tuberculosis disease status and diagnosis. Curr Opin Pulm Med 2009; 15: 181–7.

10 Marshall JC, Reinhart K; International Sepsis Forum. Biomarkers of sepsis. Crit Care Med 2009; 37: 2290–8.

11 Russell JA, Rush B, Boyd J. Pathophysiology of septic shock. Crit Care Clin 2018; 34: 43–61.

12 Jacobi J. Pathophysiology of sepsis. Am J Health Syst Pharm 2002; 59: S3–8.

13 Jeong SJ, Song YG, Kim CO et al. Measurement of plasma sTREM-1 in patients with severe sepsis receiving early goal- directed therapy and evaluation of its usefulness. Shock 2012; 37: 574–8.

14 Linder A, Christensson B, Herwald H et al. Heparin-binding protein: an early marker of circulatory failure in sepsis. Clin Infect Dis 2009; 49: 1044–50.

15 Bopp C, Hofer S, Weitz J et al. sRAGE is elevated in septic patients and associated with patient outcome. J Surg Res 2008; 147: 79–83

16 Shozushima T, Takahashi G, Matsumoto M et al. Usefulness of presepsin sCD14-ST measurements as a marker for the diagnosis and severity of sepsis that satisfied diagnostic criteria for systemic inflammatory response syndrome. J Infect Chemother 2011; 17: 764–9.

17 Sunden-Cullberg J, Norrby-Teglund A, Rouhiainen A et al. Persistent elevation of high mobility group box-1 protein HMGB1 in patients with severe sepsis and septic shock. Crit Care Med 2005; 33: 564–73.

18 Singhal N, Kumar M, Kanaujia PK et al. MALDI-TOF mass spectrometry: an emerging technology for microbial identification and diagnosis. Front Microbiol 2015; 6: 791.

19 Monneret G, Lepape A, Voirin N et al. Persisting low monocyte human leukocyte antigen-DR expression predicts mortality in septic shock. Intensive Care Med 2006; 32: 1175–83.

20 Lee SM, An WS. New clinical criteria for septic shock: serum lactate level as new emerging vital sign. J Thorac Dis 2016; 8: 1388–90.

21 Puskarich M, Trzeciak S, Shapiro N et al. Outcomes of patients undergoing early sepsis resuscitation for cryptic shock compared with overt shock. Resuscitation 2011; 82: 1289–93.

22 Boschert S. Is it Septic Shock? Check Lactate Level ACEP News. 2007. http: // (accessed 26/02/14).

23 Arnold RC, Shapiro NI, Jones AE et al. Emergency Medicine Shock Research Network (EM Shock Net) Investigators. Multicenter study of early lactate clearance as a determinant of survival in patients with presumed sepsis. Shock 2009; 32: 35–9.

24 Jones AE. Lactate clearance for assessing response to resuscitation in severe sepsis. Acad Emerg Med 2013; 20: 844–7.

25 Meziani F, Delabranche X, Asfar P et al. Bench-to-bedside review: circulating microparticles – a new player in sepsis? Crit Care 2010; 14: R236.

26 Póvoa P, Coelho L, Almeida E et al. C-reactive protein as a marker of infection in critically ill patients. Clin Microbiol Infect 2005; 11: 101–8.

27 Pradhan S, Ghimire A, Bhattarai B et al. The role of C-reactive protein as a diagnostic predictor of sepsis in a multidisciplinary Intensive Care Unit of a tertiary care center in Nepal. Indian J Crit Care Med 2016; 20: 417–20.

28 Tschaikowsky K, Hedwig-Geissing M, Braun GG et al. Predictive value of procalcitonin, interleukin-6, and C-reactive protein for survival in postoperative patients with severe sepsis. J Crit Care 2011; 26: 54–64.

29 Simon L, Gauvin F, Amre DK. Serum procalcitonin and C-reactive protein levels as markers of bacterial infection: a systematic review and meta-analysis. Clin Infect Dis 2004; 15: 206–17.

30 Petrikkos GL, Christofilopoulou SA, Tentolouris NK et al. Value of measuring serum procalcitonin, C-reactive protein, and mannan antigens to distinguish fungal from bacterial infections. Eur J Clin Microbiol Infect Dis 2005; 24: 272–5.

31 Becker KL, Snider R, Nylen ES. Procalcitonin assay in systemic inflammation, infection, and sepsis: clinical utility and limitations. Crit Care Med 2008; 36: 941–52.

32 Michael M. Update on procalcitonin measurements. Ann Lab Med 2014; 34: 263–73.

33 Hur M, Kim H, Lee S et al. Diagnostic and prognostic utilities of multimarkers approach using procalcitonin, B-type natriuretic peptide, and neutrophil gelatinase-associated lipocalin in critically ill patients with suspected sepsis. BMC Infect Dis 2014; 14: 224.

34 Jensen JU, Heslet L, Jensen TH et al. Procalcitonin increase in early identification of critically ill patients at high risk of mortality. Crit Care Med 2006; 34: 2596–602.

35 Cohen J. Current clinical controversies in the management of sepsis. J R Coll Physicians Edinb 2016; 46: 263–9.

36 Schuetz P, Chiappa V, Briel M et al. Procalcitonin algorithms for antibiotic therapy decisions: a systematic review of randomized controlled trials and recommendations for clinical algorithms. Arch Intern Med 2011; 171: 1322–31.

37 Kopterides P, Siempos II, Tsangaris I et al. Procalcitonin-guided algorithms of antibiotic therapy in the intensive care unit: a systematic review and meta-analysis of randomized controlled trials. Crit Care Med 2010; 38: 2229–41.

38 Simon P, Milbrandt EB, Emlet LL. PCT-guided antibiotics in severe sepsis. Crit Care 2008; 12: 309.

39 Kip MM, Kusters R, IJzerman J et al. PCT algorithm for discontinuation of antibiotic therapy is a cost-effective way to reduce antibiotic exposure in adult intensive care patients with sepsis. J Med Econ 2015; 18: 944–53.

40 Schuetz P, Birkhahn R, Sherwin R et al. Serial procalcitonin predicts mortality in severe sepsis patients: results from the Multicenter Procalcitonin Monitoring SEpsis (MOSES) Study. Crit Care Med 2017; 45: 781–9.

41 Schuetz P, Müeller B. Procalcitonin in critically ill patients: time to change guidelines and antibiotic use in practice. Lancet Infect Dis 2016; 16: 758–60.

42 de Jong E, van Oers JA, Beishuizen A et al. Efficacy and safety of procalcitonin guidance in reducing the duration of antibiotic treatment in critically ill patients: a randomised, controlled, open-label trial. Lancet Infect Dis 2016; 16: 819–27.

43 Nargis W, Ibrahim MD, Ahamed BU. Procalcitonin versus C-reactive protein: usefulness as biomarker of sepsis in ICU patient. Int J Crit Illn Inj Sci 2014; 4: 195–9.

44 Mann EA, Wood GI, Wade CE. Use of procalcitonin for the detection of sepsis in the critically ill burn patient: a systemic review of the literature. Burns 2011; 37: 549–58.

45 Limongi D, D’Agostini C, Ciotti M. New sepsis biomarkers. Asian Pac J Trop Biomed 2016; 6: 516–9.

46 Hanna WJ, Berrens Z, Langner T et al. Interleukin-27: a novel biomarker in predicting bacterial infection among the critically ill. Crit Care 2015; 19: 378.

47 Wu TW, Tabangin M, Kusano R et al. The utility of serum hepcidin as a biomarker for late-onset neonatal sepsis. J Pediatr 2013; 162: 67–71.

48 Simons D, Grieb G, Hristov M et al. Hypoxia-induced endothelial secretion of macrophage migration inhibitory factor and role in endothelial progenitor cell recruitment. J Cell Mol Med 2011; 15: 668–78.

49 Bozza FA, Gomes RN, Japiassú AM et al. Macrophage migration inhibitory factor levels correlate with fatal outcome in sepsis. Shock 2004; 22: 309–13.

50 Opal SM, Scannon PJ, Vincent JL et al. Relationship between plasma levels of lipopolysaccharide (LPS) and LPS-binding protein in patients with severe sepsis and septic shock. J Infect Dis 1999; 180: 1584–9.

51 Harbarth S, Holeckova K, Froidevaux C et al. Geneva Sepsis Network. Diagnostic value of procalcitonin, interleukin-6, and interleukin-8 in critically ill patients admitted with suspected sepsis. Am J Respir Crit Care Med 2001; 164: 396–402.

52 Wong HR, Cvijanovich N, Wheeler DS et al. Interleukin-8 as a stratification tool for interventional trials involving pediatric septic shock. Am J Respir Crit Care Med 2008; 178: 276–82.

53 Wang CH, Gee MJ, Yang C et al. A new model for outcome prediction in intra-abdominal sepsis by the linear discriminant function analysis of IL-6 and IL-10 at different heart rates. J Surg Res 2006; 132: 46–51.

54 Bozza FA, Bozza PT, Castro Faria Neto HC. Beyond sepsis pathophysiology with cytokines: what is their value as biomarkers for disease severity?. Memórias do Instituto Oswaldo Cruz 2005; 100: 217–21.

55 Karlsson S, Pettilä V, Tenhunen J et al. HMGB1 as a predictor of organ dysfunction and outcome in patients with severe sepsis. Intensive Care Med 2008; 34: 1046–53.

56 Delannoy B, Guye ML, Slaiman DH et al. Effect of cardiopulmonary bypass on activated partial thromboplastin time waveform analysis, serum procalcitonin and C-reactive protein concentrations. Crit Care 2009; 13: R180.

57 Li L, Zhu Z, Chen J et al. Diagnostic value of soluble triggering receptor expressed on myeloid cells-1 in critically-ill, postoperative patients with suspected sepsis. Am J Med Sci 2013; 345: 178–84.

58 Eugen-Olsen J. suPAR—a future risk marker in bacteremia. J Intern Med 2011; 270: 29–31.

59 Christ-Crain M, Morgenthaler NG, Stolz D. Pro-adrenomedullin to predict severity and outcome in community-acquired pneumonia [ISRCTN04176397]. Crit Care 2006; 10: R96.

60 Icardi M, Erickson Y, Kilborn S et al. CD64 index provides simple and predictive testing for detection and monitoring of sepsis and bacterial infection in hospital patients. J Clin Microbiol 2009; 47: 3914–9.

61 Kannan A, Selvam P. The potential of using VCS parameters of neutrophils and monocytes as an early diagnostic tool in acute bacterial infections. Nat J Lab Med 2017; 6: 2, 38–43.

62 Arendrup MC, Bergmann OJ, Larsson L et al. Detection of candidaemia in patients with and without underlying haematological disease. Clin Microbiol Infect 2010; 16: 855–62.

63 Ng PC, Li K, Chui KM et al. IP-10 is an early diagnostic marker for identification of late-onset bacterial infection in preterm infants. Pediatr Res 2007; 61: 93–8.

64 Simon L, Gauvin F, Amre DK et al. Serum procalcitonin and C-reactive protein levels as markers of bacterial infection: a systematic review and meta-analysis. Clin Infect Dis 2004; 39: 206–17.

65 Wacker C, Prkno A, Brunkhorst FM et al. Procalcitonin as a diagnostic marker for sepsis: a systematic review and meta-analysis. Lancet Infect Dis 2013; 13: 426–35.

66 Wu Y, Wang F, Fan X et al. Accuracy of plasma sTREM-1 for sepsis diagnosis in systemic inflammatory patients: a systematic review and meta-analysis. Crit Care 2012; 16: R229.

67 Kofoed K, Andersen O, Kronborg G et al. Use of plasma C-reactive protein, procalcitonin, neutrophils, macrophage migration inhibitory factor, soluble urokinase-type plasminogen activator receptor, and soluble triggering receptor expressed on myeloid cells-1 in combination to diagnose infections: a prospective study. Crit Care 2007; 11: R38.

68 Liu Y, Hou JH, Li Q et al. Biomarkers for diagnosis of sepsis in patients with systemic inflammatory response syndrome: a systematic review and meta-analysis. Springerplus 2016; 5: 2091.

69 Ajmani S, Singh H, Chaturvedi S et al. Utility of neutrophil CD64 and serum TREM-1 in distinguishing bacterial infection from disease flare in SLE and ANCA-associated vasculitis. Clin Rheumatol 2019; 38: 997–1005.

70 Gibot S, Béné MC, Noel R et al. Combination biomarkers to diagnose sepsis in the critically ill patient. Am J Respir Crit Care Med 2012; 186: 65–71.

71 Petilla V, Hynninen M, Takkunen O et al. Predictive value of procalcitonin and interleukin 6 in critically ill patients with suspected sepsis. Intensive Care Med 2002; 28: 1220–5.

72 Stryjewski GR, Nylen ES, Bell MJ et al. Interleukin-6, interleukin-8, and a rapid and sensitive assay for calcitonin precursors for the determination of bacterial sepsis in febrile neutropenic children. Pediatr Crit Care Med 2005; 6: 129–35.

73 Bozza FA, Salluh JI, Japiassu AM et al. Cytokine profiles as markers of disease severity in sepsis: a multiplex analysis. Crit Care 2007; 11: R49.

74 Flierl MA, Rittirsch D, Nadeau BA et al. Functions of the complement components C3 and C5 during sepsis. FASEB J 2008; 22: 3483–90.

75 Mauri T, Bellani G, Patroniti N et al. Persisting high levels of plasma pentraxin 3 over the first days after severe sepsis and septic shock onset are associated with mortality. Intensive Care Med 2010; 36: 621–9.

76 Huttunen R, Hurme M, Aittoniemi J et al. High plasma level of long pentraxin 3 (PTX3) is associated with fatal disease in bacteremic patients: a prospective cohort study. PLoS One 2011; 6: e17653.

Financial and Competing Interests: 
No conflict of interests declared