[Comparison of interleukin-6 and C-reactive protein serum concentrations assessment in diagnosis of infective...

Serum interleukin-6 (IL-6) level might be used to aid in diagnosis of infective endocarditis (IE), especially when blood cultures are negative. One of typical acute phase proteins is C-reactive protein (CRP), often served as an additional inflammation maker. The aim of the study was to compare serum IL-6 and CRP concentrations assessment in diagnosis and monitoring of IE. The study group consisted of 40 patients with ongoing IE and valvular heart diseases. Two control groups consisted of patients with valvular heart diseases: 15 without infection and another 15 with urinary tract infection. The diagnosis of IE was established according to the Duke University criteria; in 34 patients positive blood cultures were found. Serum IL-6 and CRP were measured on three occasions after diagnosis of IE was established and during antimicrobial treatment (mean period 14 +/- 7 days) by ELISA. Usefulness of both parameters for IE diagnosis were described. Reference values were defined as 0-12.5 pg/ml for IL-6, and 0-10 mg/l for CRP. Mean concentrations of IL-6 and CRP in patients with IE (37 +/- 44.3 pg/ml and 27.1 +/- 23.9 mg/l) were significantly higher than in controls: with urinary tract infection (9.1 +/- 4.42 pg/ml and 6.95 +/- 4.39 mg/l) and without infection (3.95 +/- 1.4 pg/ml and 2.21 +/- 0.96 mg/l). CRP concentration was not significantly correlated with IL-6 (r = 0.51, p = 0.07). The significant tendency of consecutive IL-6 concentrations to decrease (from 37 +/- 44.3 to 8.7 +/- 5.7 pg/ml), without decrease of CRP (from 27.1 +/- 23.9 mg/l to 22 +/- 18.3 mg/l) was found.

1. Elevated serum IL-6 and CRP levels may suggest ongoing IE. 2. Sensitivity, specificity, positive and negative predictive value are nonsignificantly higher for IL-6 than CRP. 3. Combined assessment of serum IL-6 and CRP concentration has no higher value in diagnosis of IE. 4, IL-6 level decrease is faster than CRP during antimicrobial treatment, and it helps better and faster monitoring of treatment.