Diagnostic efficacy of C-reactive protein and IL-6 as markers of systemic inflammation

Currently, despite widespread use of the terms “systemic inflammation” (SI) and “systemic inflammatory response” (SIR), there are no generally accepted criteria for their verification. These processes are often identified (which is methodologically incorrect) and associated with an increase in pro-inflammatory mediators in the blood. However, SI is a complex process that requires integral criteria including assessment of SIR as reactivity level, and additional SI phenomena, such as microthrombosis, systemic alteration, and distress of the neuroendocrine system. At the same time, there is a need to assess individual CB indicators as a more affordable alternative for medical practice than the use of complex integral indicators. Our objective was to evaluate diagnostic efficacy of CRP and IL-6 levels as markers of acute and chronic systemic inflammation.

The data of patients with acute critical conditions of infectious and non-infectious genesis were analyzed to study acute systemic inflammation (SI), data of patients with autoimmune diseases, chronic organ failure and other chronic destructive diseases were analyzed to study chronic systemic inflammation (ChrSI). SIR severity was evaluated by the calculation of an integral index – reactivity level (RL). Differentiation of the inflammatory process to either classical inflammation (CI), or systemic inflammation was carried out using the previously proposed scale of SI, verification of chronic systemic inflammation was performed by means of ChrSI scale. SI (or ChrSI) was revealed in all groups of patients, and the frequency of SI registration in patients with acute conditions increased with development of multi-organ failure. The frequency of SIR was higher in all groups, thus confirming inability to equate these disorders. ROC analysis showed that CRP level had poor diagnostic efficacy on the development of SI/ChrSI (AUC < 0.6), and IL-6 level had very good diagnostic value (AUC 0.8-0.9). The prognostic value of the markers for detecting the SIR was higher, with AUC_IL-6 exceeding AUC_CRP. Thus, IL-6 in many acute and chronic pathologies is sufficiently closer to integral indices than C-reactive protein with respect to diagnostic efficiency, and the dynamics of IL-6 in blood may be used to predict and evaluate complications associated with acute and chronic SI, as well as to prescribe and monitor the results of anticytokine therapy.