To investigate the clinical utility of interleukin-6 (IL-6), procalcitonin (PCT), and C-reactive protein (CRP) as predictive markers in consideration of the time-course changes in critically ill patients with organ dysfunction.
Serum levels of IL-6, PCT, CRP, and Sequential Organ Failure Assessment (SOFA) scores were measured sequentially in 92 patients during their initial 5 days following admission to the intensive care unit. Maximum values were analyzed. Patients were assigned to a low ( ≤ 8), intermediate ( > 8 and ≤ 16), or high ( > 16 and ≤ 24) SOFA score group.
There were significant differences in the maximum serum levels of IL-6 and PCT among the three SOFA score groups (IL-6, P < 0.0001; PCT, P = 0.0004). Specifically, comparisons between the groups revealed significant differences in IL-6 levels (low versus intermediate, P = 0.0007; intermediate versus high, P = 0.0010). The probability of patients with the maximum value was greatest on day 1 (56.5%) for IL-6, on day 1 (39.1%) or day 2 (38.0%) for PCT, on day 3 (39.1%) for CRP, and on day 1 (43.5%) for SOFA score. The median (interquartile range) peak day of IL-6 was day 1 (1–2), which was significantly earlier than that of SOFA score at day 2 (1–3) (P = 0.018).
Serum levels of IL-6 reflected the severity of organ dysfunction in critically ill patients most accurately compared to PCT and CRP. Interleukin-6 elevated soonest from the insult and reached its peak earlier than SOFA score.
IL-6 reflected SOFA score more accurately and increased earlier than PCT or CRP. IL-6 is useful to assess severity in the early phase of critical illness.