1. Role of Biomarkers in Sepsis
(Follow up on Non-Culture Methods for Sepsis)
N. Naidoo
2. The next slide should define all these terms.
Unless the 2nd slide (4) from this one is the
one in which you will define the terms!!
3. Term Definition
Infection invasion of a host organism's bodily tissues by disease-causing
organisms, their multiplication, and the reaction of host tissues
to these organisms and the toxins they produce
Bacteremia The presence of viable bacteria in circulating blood
Systemic Inflammatory Response
Syndrome (SIRS)
Temperature > 38°C or < 36°C
Heart rate > 90 beats/min
Respiratory rate > 20 breaths/min or PaCO2 < 32 mm Hg
WBC count > 12,000/mm3 , < 4000/mm3 , or > 10% immature
(band) forms.
Sepsis The systemic inflammatory response to infection. It should be
determined whether they are a direct systemic response to the
presence of an infectious process and represent an acute
alteration from baseline in the absence of other known causes
for such abnormalities.
Wang P, Yang Z, He Y, Shu C. Pitfalls in the rapid diagnosis of positive blood culture. Rev. Med. Microbiol. 21(3), 39–43 (2010).
4. Severe Sepsis/SIRS. Sepsis (SIRS) associated with organ dysfunction,
hypoperfusion, or hypotension. Hypoperfusion and
perfusion abnormalities may include, but are not limited to,
lactic acidosis, oliguria, or an acute alteration in mental
status.
Refractory (Septic) Shock/SIRS
Shock.
A subset of severe sepsis (SIRS) and defined as sepsis (SIRS)
induced hypotension despite adequate fluid resuscitation along
with the presence of perfusion abnormalities that may include,
but are not limited to, lactic acidosis, oliguria, or an acute
alteration in mental status. Patients receiving inotropic or
vasopressor agents may no longer be hypotensive by the time
they manifest hypoperfusion abnormalities or organ dysfunction,
yet they would still be considered to have septic (SIRS) shock.
Multiple Organ Dysfunction
Syndrome (MODS).
Presence of altered organ function in an acutely ill patient such
that homeostasis cannot be maintained without intervention.
Wang P, Yang Z, He Y, Shu C. Pitfalls in the rapid diagnosis of positive blood culture. Rev. Med. Microbiol. 21(3), 39–43 (2010).
5. TRANSIENT BACTEREMIA
• generally lasting for a few minutes or a few hours, is
associated with procedures involving
• anatomic sites colonized by normal microbial flora (i.e.,
after colonoscopy, percutaneous catheterization, or
dental extractions) or with a manipulation of localized
infected sites (i.e., furuncles).
INTERMITTENT BACTEREMIA
• typically associated with closed-space infections, such
as abscesses, or with focal infections,
• such as pneumonia and osteomyelitis.
• It is defined as recurrent episodes of bacteremia due to
the same microorganism intermittently detected in blood
because of cyclical clearance and recurrence of the
pathogen at the primary site of infection.
CONTINOUS BACTEREMIA
• persistent low-grade bacteremia is commonly
• associated with an intravascular focus of infection such
as infective endocarditis (IE) or vascular-graft infections.
In all cases the microbial load may be as low as 1 CFU/
ml, making the microbiological diagnosis difficult
Wang P, Yang Z, He Y, Shu C. Pitfalls in the rapid diagnosis of positive blood culture. Rev. Med. Microbiol. 21(3), 39–43 (2010).
6. Wang P, Yang Z, He Y, Shu C. Pitfalls in the rapid diagnosis of positive blood culture. Rev. Med. Microbiol. 21(3), 39–43 (2010).
7. Angus DC, Linde-Zwirble WT, Lidicker J, Clermont G, Carcillo J, Pinsky MR. Epidemiology of severe sepsis in the United States: analysis of incidence, outcome, and
associated costs of care. Crit. Care Med. 29(7), 1303–1310 (2001).
8. SIRS
systemic inflammatory response
syndrome
– systemic pro-inflammatory mediators
(primarily TNF, IL-1, IL-6) predominate
over anti-inflammatory mediators.
MARS
mixed antagonist response syndrome
– surges of SIRS and CARS
CARS
Compensatory anti-inflammatory
syndrome
compensatory anti-inflammatory
syndrome
– systemic anti-inflammatory
mediators (IL-4, IL-10, IL-11, IL-13,
soluble TNF receptors, IL-1 receptor
antagonists, and others) predominate
over pro-inflammatory mediators.
Desmet SS. The problem of sepsis – an expert report of the European-Society-Of-Intensive-Care-Medicine. Intensive Care Med. 20(4), 300–304 (1994).
9. The Relationships between SIRS, MARS and CARS
What is the Title of the slide?
Desmet SS. The problem of sepsis – an expert report of the European-Society-Of-Intensive-Care-Medicine. Intensive Care Med. 20(4), 300–304 (1994).
12. FEVER
• temperature greater than 38.0 .C is considered fever, and
fever is typically defined as a pyrogen-mediated rise in body
temperature above this temperature.
•
• Physiologically, it has been defined as “a state of elevated
core temperature, which is often, but not necessarily,
• part of the defensive responses of multicellular organisms
(host) to the invasion of live
•
• (micro-organisms) or inanimate matter recognized as
pathogenic or alien by the host
•
• The elevated body temperature during fever should be
distinguished from that occurring in hyperthermia.
Pierrakos C, Vincent JL. Sepsis biomarkers: a review. Crit. Care 14(1), R15 (2010).
13. FUNCTION OF FEVER
• different studies showing both potentiating and inhibitory effects of the response to infection.
• Phylogenetic studies have shown that fever is widespread within the animal kingdom; as the rise in
temperature is metabolically expensive but still is well-preserved in evolution,
• it has been argued that fever has to be an adaptive and beneficial response.
• Animal studies have demonstrated enhanced resistance to infection during experimentally increased
temperature.
• In human in vivo studies associations between higher temperatures and better disease outcome have
been observed.
• On the contrary, it has been suggested that pyrogenic cytokines such as IL-1, IL-2 and TNF are involved in
at least part of the local and systemic response to infection, with higher levels of circulating cytokines
correlating with less favorable outcome.
Pierrakos C, Vincent JL. Sepsis biomarkers: a review. Crit. Care 14(1), R15 (2010).
14. PYROGENS
Endogenous Pyrogens • Most exogenous pyrogens are microbes, toxins or other microbial
products,
• either working directly on the hypothalamus or inducing the release of
endogenous pyrogens,
• derived form the host’s cells.
Exogenous Pyrogens • Endogenous pyrogens, most importantly IL-1, IL-6, TNF-α and IFN-γ,
interact
• with brain microglia and brain endothelial receptors, thus activating the
arachidonic acid
• pathway. This in turn results in the production of cyclo-oxygenase
derived prostaglandins,
• prostacyclins and thromboxane. Prostaglandin E2, most notably,
increases the hypothalamic thermostatic setpoint
23. PCT• Procalcitonin (PCT) is a propeptide of calcitonin that is ubiquitously expressed as part of the host’s inflammatory response to a
variety of insults
• Although calcitonin is a hormone classically produced in the parathyroids and involved in calcium homeostasis, PCT (one of the
calcitonin precursors) has effects on a variety of inflammatory conditions, including cardiogenic shock, trauma, necrotizing
pancreatitis, burns, surgery, and infection
• A growing body of evidence suggests that PCT is a marker of severe bacterial infection and can distinguish patients who have sepsis
from patients who have SIRS
• In particular, PCT levels in plasma have been correlated with sepsis-related organ failure scores and may be useful in risk assessment
• High and persistent elevations in PCT levels have been associated with poor outcomes for ICU patients
• There seems to be particular value of PCT in risk assessment for pediatric patients
• Although several studies suggested that PCT is among the most promising biomarkers for sepsis, considerable controversy
surrounding its clinical usefulness still remains.
• A recent meta-analysis indicated that PCT cannot reliably differentiate sepsis from other noninfectious causes of SIRS in critically ill
adult patients.
• However, the U.S. Food and Drug Administration (FDA) has approved the use of PCT in conjunction with other laboratory findings to
aid the risk assessment of critically ill patients.
Pierrakos and Vincent: Sepsis biomarkers: a review. Critical Care 2010 14:R15.
24. Procalcitonin for the Guidance of Antibiotic Therapy in
Lower Respiratory Tract Infections
• Numerous studies have evaluated PCT as a biomarker to guide initiation of antibiotic therapy in patients suspected of LRTIs
• A meta-analysis published in 2011 with 8 studies (3431 patients) showed a reduction in antibiotic prescription in the PCT-guided
antibiotic treatment groups by 30%
• As PCT levels increase upon bacterial infection and decrease upon recovery, it can be used to guide antibiotic therapy in
individual patients as a surrogate biomarker.
• Two low PCT measurements, over the first 4 to 6 hours of hospital admission, resulted in fewer patients started on empirical
antibacterials. Low PCT levels over the first 4 hours of inpatient care have an excellent negative predictive value for bacterial
infection
• A Cochrane review published in 2012 with 14 studies (4221 participants) showed that PCT guidance was not associated with
increased mortality (5.7% versus 6.3%, or treatment failure (19.1% versus 21.9%). Total antibiotic exposure was significantly
reduced overall.
• To date, numerous studies (including meta-analysis) have been published and provide consistent results that withhold antibiotic
prescription can be done with low levels of PCT
Pierrakos and Vincent: Sepsis biomarkers: a review. Critical Care 2010 14:R15.
25. Procalcitonin for Antibiotic Guidance in Other
Infections
• Procalcitonin has been studied in febrile neutropenic patients, fungal infections, postoperative
fever, arthritis, endocarditis, meningitis, and suspected bloodstream infections
• The majority of published studies were observational and it remains uncertain whether PCT can
be safely used for antibiotic guidance in different settings.
• For some infections, PCT may not be sensitive enough for routine clinical use.
• In a recent meta-analysis with 6 trials (1006 episodes of suspected endocarditis), the global
measures of accuracy of CRP were higher than PCT showing that current evidence does not
support the routine use of serum PCT or CRP to rule in or rule out endocarditis
Pierrakos and Vincent: Sepsis biomarkers: a review. Critical Care 2010 14:R15.
26. Procalcitonin for Identification of Sepsis
• Procalcitonin has been studied to differentiate between sepsis and SIRS of noninfectious origin.
• Numerous studies have investigated the diagnostic usefulness of PCT, comparing it with CRP. Initially, PCT was found more sensitive and
specific than CRP for bacterial infection
• In a meta-analysis of Uzzan et al. (publication date:2006), 33 studies published between April, 1996, and October, 2004, were included,
with 3,943 patients (1,825 patients with sepsis, severe sepsis, or septic shock and 1,545 with only SIRS). This meta-analysis showed that the
ROC for PCT was higher than for CRP for identification of sepsis (0.78 versus 0.71, �� = 0.02). However, the investigators restricted the
population to surgery or trauma patients. Therefore, no conclusion can be drawn for patients other than surgical
• A posterior meta-analysis (2007) looking at the diagnostic accuracy of PCT in sepsis diagnosis in critically ill patients included 18 studies
published between April, 1996, and November, 2005, with very restrictive inclusion criteria, including evidence of infection by any
microbiological test. Uzzan et al. concluded that PCT was not able to discriminate between sepsis and SIRS. The diagnostic accuracy of PCT
was low, mean sensitivity and specificity were both 71% (95% CI 67–76), and AUROC was 0.78 (95% CI 0.73–83).
• However, their findings were heavily biased because of their selection criteria. The rejection of such studies has been raised as a major
criticism of their conclusion that PCT cannot accurately distinguish sepsis from SIRS in critically ill patients
• The most recent meta-analysis published by Tang et al. included 30 studies (3244 patients) until February 2012.They concluded that
accuracy of PCT to discriminate sepsis and SIRS was low, mean sensitivity 77% (95% 72–81), and specificity 79% (95% CI 74–84).
• Although PCT has been shown to correlate closely with infection, it has some limitations. It rises transiently in patients with nonseptic
conditions and SIRS (e.g., trauma, surgery, and heatstroke) and is not detectable in certain cases of sepsis
Pierrakos and Vincent: Sepsis biomarkers: a review. Critical Care 2010 14:R15.
28. TREM-1
• Neutrophils and monocytes/macrophages are the primary mediators of the innate immune response to bacterial infection, promoting the
release of proinflammatory cytokines such as TNF- and IL-1b, which, when produced in excess, contribute to end-organ dysfunction and
overwhelming sepsis.
• The so-called triggering receptor expressed on myeloid cells 1 (TREM-1) is part of the immunoglobulin superfamily and is upregulated in
response to bacteria or fungi.
• When bound to ligand, TREM-1 stimulates the release of cytokines.
• In contrast to infections, TREM-1 is not upregulated in noninfectious inflammatory disorders such as inflammatory bowel
• disease and SIRS
• A soluble form of TREM-1 (sTREM-1) is shed from the membranes of activated phagocytic cells and can be quantified in human body fluids.
• Several studies have investigated the use of TREM-1 as a diagnostic biomarker and have shown it to be more sensitive and specific than CRP
and PCT
• Although TREM-1 may be a promising diagnostic marker for sepsis, less is presently known about its use in risk assessment and prognosis for
patients with known sepsis.
• Overall, the present data suggest that IL-6 and CRP are sentinel markers of inflammation and infection but are too nonspecific for further
clinical use. PCT will likely enhance clinicians’ risk assessments for critically ill patients with sepsis.
• Furthermore, TREM-1 is an additional promising candidate. Given the high complexity and variability of the disease, biomarker panels or
composite markers may prove most useful in examining a particular immunological pathway, predicting organ- specific responses, and, ideally,
identifying at-risk individuals
Pierrakos and Vincent: Sepsis biomarkers: a review. Critical Care 2010 14:R15.
29. suPAR
• The soluble form of urokinase-type plasminogen activator receptor (suPAR) is a new biological marker of immunologic
activation Urokinase-type plasminogen activator receptor (uPAR) is expressed on various cell types and participates
in numerous immunologic functions including migration, adhesion, angiogenesis, fibrinolysis, and cell proliferation.
• uPAR/uPA system participated in migration of inflammatory cells from the bloodstream into tissues against infection.
During inflammatory stimulation, uPAR is cleaved from the cell surface by proteases to create the soluble form of the
receptor, suPAR, which can be detected in blood, urine, and cerebrospinal fluid
• Measurements can be obtained from commercial ELISA kits; suPAR measurements also are included in multiplex
assays together with cytokines.
• High serum suPAR concentrations have also been found to predict mortality in patients with active tuberculosis and
other diseases associated with an inflammatory response
• Some studies have showed that suPAR levels were elevated in acutely ill patients but that their diagnostic value was
not superior to other biomarkers such as CRP, PCT, or sTREM-1
• Recently, two studies evaluating diagnostic accuracy of suPAR have shown specificity from 64–77%
Pierrakos and Vincent: Sepsis biomarkers: a review. Critical Care 2010 14:R15.
30. Pro-ADM
• Adrenomedullin (ADM) is a 52-amino-acid peptide with immune modulating, metabolic, and vasodilator activity.
• Its widespread production in the tissues helps to maintain a blood supply in every organ. Moreover, ADM has a bactericidal
activity and could be helpful in the evaluation of sepsis diagnosis and prognosis and in monitoring such conditions
• Prohormone fragments (pro-ADM) are more stable than the complete peptide and their levels can be measured in biological
fluids - it has been detected in plasma of patients with septic shock as a consequence of the ADM active peptide degradation
• Pro-ADM is a biomarker of prognostic value and could be used to identify more severe patients with pneumonia and/or
needing ICU care
• In a recent single prospective observational study conducted in a Spanish adult intensive care unit (137 patients), pro-ADM
showed a significant dose-response trends to predict hospital mortality (OR = 3.00, 95% CI 1.06–8.46) compared to PCT
and CRP.
• However, the prognostic accuracy was better for severity scores than for any biomarker
• In an Italian study comparing PCT and MR-pro-ADM
• in 200 septic patients, 90 patients with SIRS, and 30 healthy individuals, the pro-ADM distinguished septic patients.
• Moreover, the combined use of PCT and MR-pro-ADM gave a posttest probability of 0.998 in the cohort of all septic patients.
The combination of biomarkers may substantially improve the early diagnosis of sepsis
Pierrakos and Vincent: Sepsis biomarkers: a review. Critical Care 2010 14:R15.
31. Presepsin.• CD14 is a glycoprotein expressed on the membrane surface of monocytes and macrophages and serves as a receptor for
(LPSs) and LPS-binding proteins (LPBs).
• By activating a proinflammatory signaling cascade on contact with infectious agents, CD14 has a role as a recognition
molecule in the innate immune response against microorganisms.
• During inflammation, plasma protease activity generates soluble CD14 (sCD14) fragments. One of them is called presepsin,
and is normally present in very low concentrations in the serum of healthy individuals and has been shown to be increased in
response to bacterial infections
• In a multicenter prospective study (106 patients with
• suspected sepsis or septic shock were included and 83 SIRS patients without infection), elevated concentrations of preseason
were observed in septic patients compared to control patients.
• The best diagnostic cutoff for presepsin was
• 600 pg/mL with sensitivity of 78.95% (95% CI, 69.4 to 86.6)
• and specificity of 61.90% (95% CI, 50.7 to 72.3).
• There was no difference between levels of presepsin and sepsis severity.
• Although presepsin showed a significant prognostic value and initial values were significantly correlated with in-hospital
mortality of patients affected by sepsis, severe sepsis, or septic shock, two recent studies have shown that presepsin is an
useful biomarker for early diagnosis of sepsis and evaluation of prognosis in septic patients (sensitivity: 71-72%, specificity:
70–86%, and NPV: 52–71%)
Pierrakos and Vincent: Sepsis biomarkers: a review. Critical Care 2010 14:R15.
32.
33. Serum Amyloid A
Serum amyloid A (SAA) is an apolipoprotein reported to have potential for diagnosing sepsis.[4,28] SAA is expressed at levels up to 1000-times higher after 8–24 h from
the onset of sepsis.[4,69] Compared with CRP levels, SAA levels are reported to rise faster and higher after the onset of sepsis and remain at higher relative elevations.[28]
Similar to PCT and CRP, studies using SAA have reported various DA values and CVs (Table 2), likely a result of the different assays used, as well as the development
of assays with lower detection limits. Serum SAA levels of less than 15 mg/l for the elderly over 65 years and less than 10 mg/l for adults and newborns aged 3–7 days
are indicative of healthy states
hough SAA is mainly studied as a biomarker for bacterial infection, a recent study by Kajiya et al. on patients with viral infections reported elevated SAA levels above
healthy cutoff of 10 mg/l among the infected patients.[47] However, SAA may not be clinically useful because it may be too sensitive, as it has been reported to
rease during minor viral infections and in patients not presenting symptoms.[47]
35. Conclusions
• (1) Bloodstream infection is a serious life-threatening condition with high mortality. In some cases,
the diagnosis is challenging. An early diagnosis of sepsis helps to enable rapid treatment, improve
outcomes, and reduce unnecessary antibiotic therapy.
• (2) Choosing the correct empiric therapy is sometimes a difficult process. The emergence of
resistant pathogens is consequence of irrational use of antibiotics.
• (3) PCT and PCR are widely used in clinical practice and are more useful to rule out infection. PCT
is the most studied biomarker that guides early stopping of antibiotic therapy in adults.
• (4) New biomarkers are being evaluated in different clinical scenarios, although none of them have
shown sufficient sensitivity or specificity to rule out infection.
• (5) Presepsin appears to be the most promising new biomarker for early diagnosis of sepsis and
better prognostic performance than procalcitonin.
36. Conclusions
The main challenge facing future biomarker research, and in reviewing biomarker studies, is the lack of standard operating protocols for each
specific biomarker. There is high variability in study designs, including small sample sizes,[16,21,27,34,37–40,43–46,48,62,73] heterogeneous population types,
[27,33,34,46] population type specificity[21,37,39,45,46,62] and high variation in assay equipment. Several studies also suffer from poor presentation and/or
application of statistical analysis of data,[4,16,21,27,33,34,37,38,40,41,43–45,48,53,62] which may lead to improper interpretation of results by the readers. Many studies
are single-centre studies involving small sample sizes, which may result in incorrect representation of the general population, but this restriction is a
result of the high costs of running studies in the clinical setting and incorporating multiple centres. However, other issues pertaining to study design
require the establishment of standardization among biomarker research studies.[17,22,58] Efforts have already been made to establish reporting and
analysis standards, such as Standards for Reporting of Diagnostic Accuracy[81,82] and Grading of Recommendations Assessment, Development and
Evaluation,[83,84] and the research community should endeavour to adopt these standards on a global scale for all future studies.
37. Conclusions
Key Issues
• C-reactive protein, procalcitonin and serum amyloid A are promising diagnostic biomarkers of bacterial infection requiring further in-depth
research to verify their diagnostic relevancies.
• Mannan and antimannan antibodies are potentially useful biomarkers of fungal infection but their assays are prone to false-positives and -
negatives, requiring combination with other assays.
• IFN-γ-inducible protein 10 is a relatively new, promising diagnostic and prognostic biomarker of several different viral infections, needing
more studies on its relevancy.
• Many other potential biomarkers of sepsis have been identified; effort should be made to conduct thorough research on existing biomarkers
instead of searching for one 'perfect' biomarker.
• No singular 'ideal' biomarker of sepsis has been identified; a more effective, alternative strategy may be to combine multiple markers.
• Assays for current sepsis biomarkers, especially procalcitonin, are too varied and lack the detection limits to produce consistent, accurate
results.
• Future sepsis biomarker research requires multicentre studies, methodology standardization and more rigorous assays.
• Development of a multiplex point-of-care testing kit may help overcome many of the existing issues of current studies.