Procalcitonin and interleukin 6 for predicting blood culture positivity in sepsis

Procalcitonin and interleukin 6 (IL-6) are well-known predictors of blood culture positivity in patients with sepsis. However, the association of procalcitonin and IL-6 with blood culture positivity was assessed separately in previous studies. This study aims to examine and compare the performance of procalcitonin and IL-6, measured concomitantly, in predicting blood culture positivity in patients with sepsis.

Forty adult patients with sepsis were enrolled in the study. Blood cultures were drawn before the institution of antibiotic therapy. The area under the curve (AUC) of the receiver operating characteristic curve was estimated to assess the performance of procalcitonin and IL-6 in predicting blood culture positivity.

Positive blood cultures were detected in 10 patients (25%). The AUC of procalcitonin and IL-6 was 0.85 and 0.61, respectively. The combined performance of procalcitonin and IL-6 was similar to that of procalcitonin alone, AUC of 0.85. On univariate analysis, only procalcitonin and IL-6 were associated with blood culture positivity. Multivariate logistic regression analysis showed that only procalcitonin was associated with blood culture positivity (odds ratio, 12.15 [1.29-114.0] for levels above the median compared with levels below the median). Using procalcitonin cut points of 1.35 and 2.14 (nanogram per milliliter) enabled 100% and 90% identification of positive blood cultures and reduced the need of blood cultures by 47.5% and 57.5%, respectively.

Compared with IL-6, procalcitonin better predicts blood culture positivity in patients with sepsis. Using a predefined procalcitonin cut points will predict most positive blood cultures and reduce the need of blood cultures in almost half of patients with sepsis.