Procalcitonin versus C-reactive protein and immature-to-total neutrophil ratio as markers of infection after cardiopulmonary bypass in children.

OBJECTIVE: To document concentrations of procalcitonin (PCT), C-reactive protein (CRP), and immature-to-total neutrophil ratio (ITR), postcardiopulmonary bypass (CPB), and to test the hypothesis that PCT is a more reliable marker of infection than CRP or ITR in the post-CPB child.

DESIGN: Prospective cohort study.

SETTING: Pediatric intensive care units at Royal Children's Hospital, Melbourne, Australia and Birmingham Children's Hospital, UK.

PATIENTS: First stage: 283 post-CPB children; second stage: 65 post-CPB children with suspected infection.

INTERVENTIONS: In the first stage, PCT, ITR, and CRP were measured serially on the first, second, third, and fifth postoperative day (POD). In the second stage, PCT, ITR, and CRP were measured in the specimens taken in the period before and after the clinical diagnosis of infection.

MEASUREMENTS AND MAIN RESULTS: In children without infection, the median peak PCT concentration more than 5 PODs was 1.0 ng/mL, in children with local infection 1.0 ng/mL, and in children with definite sepsis 14.8 ng/mL. CRP increased in all subgroups of children studied, reaching a peak on POD 3 (median 51 mg/L). In definite sepsis, CRP was increased more than the other subgroups. ITR remained high with a median of 0.08 from POD 1 and gradually decreased, except in definite sepsis, where it remained high. In a receiver operating characteristic curve analysis, PCT was the most reliable variable for the diagnosis of probable/definite sepsis with area under the curve 0.84 (95% confidence interval, 0.75-0.92) compared with 0.73 (0.62-0.84) for ITR and 0.62 (0.52-0.73) for CRP.

CONCLUSIONS: CRP was a poor marker of sepsis in this study. Children with a PCT <2.2 ng/mL or ITR <0.08 were unlikely to have definite or probable sepsis. However, only a third of children with high values of PCT and ITR had definite or probable sepsis.