Background--Variability in the clinical presentation of infective endocarditis (IE) makes the diagnosis a clinical challenge. We hypothesized that serum procalcitonin, a marker of systemic bacterial infection, might be helpful in its diagnosis.

Methods and Results--We conducted a prospective cohort study in 67 consecutive patients admitted to the hospital with the suspicion of IE or in whom the suspicion arose during the hospital course. IE was diagnosed by an interdisciplinary team that included an infectious disease specialist and a cardiologist who applied the Duke criteria. IE was confirmed in 21 patients. Procalcitonin was significantly higher in patients with IE (median 6.56 ng/mL) than in those with other final diagnoses (median 0.44 ng/mL, P<0.001). The area under the receiver operating characteristic curve that used procalcitonin to predict IE was 0.856 (95% CI 0.750 to 0.962), compared with 0.657 (95% CI 0.511 to 0.802) for C-reactive protein. The optimum concentration of procalcitonin for the calculation of positive and negative predictive accuracy as obtained from the receiver operating characteristic curve was 2.3 ng/mL. With this cutoff, the test characteristics of procalcitonin were as follows: sensitivity 81%, specificity 85%, negative predictive value 92%, and positive predictive value 72%. Multiple logistic regression analysis revealed that procalcitonin was the only significant independent predictor of IE on admission (OR 1.52, 95% CI 1.07 to 2.15, P=0.018).

Conclusions--Procalcitonin may be a valuable additional diagnostic marker in patients with suspected IE.