How are infectious causes of systemic inflammatory response syndrome (SIRS) differentiated from noninfectious causes?

Updated: Nov 12, 2020
  • Author: Kamran Boka, MD, MS; Chief Editor: Michael R Pinsky, MD, CM, Dr(HC), FCCP, FAPS, MCCM  more...
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A significant amount of research has evaluated the use of acute-phase reactants to help differentiate infectious from noninfectious causes of systemic inflammatory response syndrome (SIRS). Several studies have found plasma procalcitonin (PCT) levels to be useful in this regard. [22]

In an observational, prospective study in a pediatric ICU, Arkader et al showed that PCT levels could be used to differentiate between infectious and noninfectious SIRS, while C-reactive protein (CRP) levels could not. In this study, PCT levels were increased at admission (median 9.15 ng/mL) in all 14 patients with bacterial sepsis, whereas CRP levels were increased in only 11 of the 14. In addition, PCT levels, but not CRP levels, subsequently decreased in most patients who progressed favorably. [23]

A review of PCT and CRP, as well as IL-6 and protein complement 3a (C3a), by Selberg et al showed that PCT, IL-6, and C3a were more reliable in distinguishing SIRS from sepsis. Plasma concentrations of PCT, C3a, and IL-6 obtained up to 8 hours after clinical onset of sepsis or SIRS were significantly higher in septic patients; the median PCT was 3.0 ng/ml in patients with SIRS, versus 16.8 ng/mL in patients with sepsis. [24]

A study by Balci et al confirmed that PCT is a better indicator of early septic complications than CRP is in complex populations, such as patients with multiple trauma. [25] Hohn et al recently demonstrated, in the ICU, that sepsis protocols using PCT to determine antibiotic utilization was associated with decreased duration of antibiotic therapy without compromising patient outcomes. [26]

Caution must be used in interpreting PCT results in elderly patients. Lai et al demonstrated that PCT is useful in predicting bacteremia in elderly patients but was not an independent marker for local infections. [27] There is also current debate regarding appropriate cut-off levels for PCT at which they are significant.

PCT is becoming increasingly available to physicians as a point-of-care test. Currently, availability of this assay will vary by medical center.

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