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Circulating complement proteins for differentiation of SIRS and sepsis


The systemic inflammatory response of the body to invading microorganisms, termed sepsis, leads to profound activation of the complement (C) system. The main proinflammatory properties of the complement system can be attributed to the anaphylatoxins C3a, C4a, C5a. These polypeptides are generated after proteolytic cleavage of the α-chain of C3, C4 or C5. The present study was conducted to determine serum complement 3 and 4 levels for differentiation in patients with SIRS and sepsis, in comparison with C-reactive protein (CRP), thrombocyte and leukocyte counts.


Fifty-eight patients with SIRS and 41 patients with sepsis were admitted to the study. Blood samples were taken at the first day of intensive care unit for analysis of C3, C4, CRP, thrombocyte and leukocyte counts.


Thrombocyte count was significantly lower in septic patients (mean ± SE: 179,975 ± 14,932, P = 0.005) compared with SIRS patients (243,165 ± 16,243). The plasma concentrations of CRP, C3 and C4 level were not different between groups. The power of parameters to discriminate between septic and SIRS patients was determined in a receiver operating characteristic analysis. Thrombocyte was the best analysis to differentiate between both populations with a maximal sensitivity and specificity (Table 1).

Table 1 Best cutoff values, area under the curve (AUC) (mean ± SE), sensitivity and specificity of all variables to differentiate patients with sepsis from patients with SIRS


In this study, C3, C4 and CRP had poor sensitivity and specificity for the differentiation of SIRS and sepsis. Because of the complex pathophysiology involved, it is likely that not a single mediator but a panel of different inflammatory mediators will ultimately predict the outcomes of individual patients.


  1. Selberg O, Hecker H, Martin M, et al.: Crit Care Med 2000, 28: 2793-2798. 10.1097/00003246-200008000-00019

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Sungurtekin, H., Balcý, C. & Sungurtekin, U. Circulating complement proteins for differentiation of SIRS and sepsis. Crit Care 7, P031 (2003).

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  • Intensive Care Unit
  • Polypeptide
  • Inflammatory Mediator
  • Leukocyte Count
  • Septic Patient