Evaluation of serum cytokine concentrations in patients with infective endocarditis

Early diagnosis of infective endocarditis is important for clinical outcome, as mortality increases if diagnosis is delayed. Diagnosis is based on clinical features, echocardiography and blood culture findings, but negative blood cultures have been reported in 5-15% of proven cases. The study aim was to investigate serum cytokine levels in patients with infective endocarditis, and the possible use of these data in diagnosis and monitoring of the disease.

The study group comprised 40 patients with acquired rheumatic valvular heart disease and ongoing infective endocarditis. A diagnosis of infective endocarditis was established by clinical examination, echocardiography, laboratory investigations (inflammatory parameters) and positive blood cultures (n = 34). Two control groups included patients with acquired rheumatic valvular heart disease: 15 without infective endocarditis, and 15 with active urinary tract infection with significant bacteriuria. Serum interleukin-1alpha (IL-1alpha), interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha) levels were measured on three occasions during antimicrobial treatment (mean period 14 +/- 7 days).

Serum IL-1alpha and TNF-alpha levels were not elevated in the study group, or in controls (IL-1alpha <3.9 pg/ml; TNF-alpha <10 pg/ml). Serum IL-6 levels were elevated on all occasions in patients with infective endocarditis (first measurement: 37.0 +/- 44.3 pg/ml; second 18.7 +/- 16.4; third 8.5 +/- 5.2) with a significant tendency to decrease during treatment (p <0.01, ANOVA). In all controls without infection the serum IL-6 concentrations were below calibration range (<3.2 pg/ml). In the control group with active urinary tract infection, IL-6 concentrations were slightly (but not significantly) elevated (4.49 +/- 1.82 pg/ml, p = NS).

Elevated serum IL-6 levels may suggest ongoing infective endocarditis and might be used to aid in diagnosis and monitoring of treatment of the disease. Serum IL-1alpha and TNF-alpha levels were not affected. A further understanding of the role of serum cytokine concentrations in the diagnosis, prognosis and monitoring of infective endocarditis might be valuable in clinically uncertain diagnoses, especially when blood cultures are negative.