Fever is one of the most common conditions requiring the attention of the pediatrician. The evaluation of an infant with febrile illness and no obvious focus of infection is a challenging task and can be expensive, time-consuming and invasive. The general condition of the infant can be deceptive and does not assist reliably in clinical differentiation of a low risk versus high risk bacterial infection(1). This is compounded by the fact that no single laboratory test has been shown to identify infants with serious bacterial infection (SBI). Laboratory markers which have been used to predict SBI include raised white blood cell (WBC) counts, C-reactive protein (CRP), procalcitonin (PCT) and even interleukin-6 levels(2). WBC count, though easily available and used widely as a predictor of SBI, by itself, does not compare well with relatively more recent markers like CRP and PCT.

In this issue of Indian Pediatrics, Fouzas and colleagues(5) have estimated the incidence of reactive thrombocytosis among febrile infants and assessed the utility of platelet count as a potential predictor of SBI in these patients. The study is a retrospective analysis of case-records of 408 infants aged 29-89 days with fever without a focus of infection. All patients had sepsis evaluation including blood counts, culture, urine microscopy and culture and CRP estimation. Chest radiographs, stool culture and lumbar puncture for cerebrospinal fluid examination had been performed when indicated. Thus the results of standard investigations of sepsis were available. SBI was documented in 103 (25.2%) of the infants. The mean platelet count in SBI infants was observed to be significantly higher than non-SBI infants. However, no single cut-off value could be ascertained due to overlap of platelet counts between the two groups. A discriminatory threshold of >450,000/µL platelet count as a single parameter had comparable specificity and sensitivity with other laboratory tests. Taken singly it offered no advantage over existing markers of SBI. Addition of platelet count >450,000/µL to a combination of other predictive parameters i.e. WBC³15,000/µL, pyuria ³10 WBC/hpf and CRP ³2mg/dL significantly improved sensitivity.