Leukopenia, neutropenia, and procalcitonin levels in young febrile infants with invasive bacterial infections.

ABSTRACT

BACKGROUND AND OBJECTIVE: Serum procalcitonin (PCT) is a highly accurate biomarker for stratifying the risk of invasive bacterial infections (IBIs) in febrile infants ≤60 days old. However, PCT is unavailable in some settings. We explored the association of leukopenia and neutropenia with IBIs in non-critically ill febrile infants ≤60 days old, with and without PCT. METHODS: We conducted a secondary analysis of a prospective observational cohort consisting of 7407 non-critically ill infants ≤60 days old with temperatures ≥38°C. We focused on the risk of IBIs in patients with leukopenia (white blood cell [WBC] count <5000 cells/µL) or neutropenia (absolute neutrophil count [ANC] <1000 cells/µL), categorized to extremes of lower values, and the impact of PCT on these associations. Multiple logistic regression was used to identify independent predictors of IBIs. RESULTS: Final analysis included 6865 infants with complete data; 45% (3098) had PCT data available. Of the 6865, a total of 111 (1.6%) had bacteremia without bacterial meningitis, 18 (0.3%) had bacterial meningitis without bacteremia, and 19 (0.3%) had both bacteremia and bacterial meningitis. IBI was present in four of 20 (20%) infants with WBC counts ≤2500 cells/µL and four of 311 (1.3%) with ANC <1000 cells/µL. In multivariable logistic regression analysis not including PCT, a WBC count <2500 cells/µL was significantly associated with IBI (OR 13.48, 95% CI 2.92-45.35). However, no patients with leukopenia or neutropenia and PCT ≤0.5 ng/mL had IBIs. CONCLUSIONS: Leukopenia ≤2500 cells/µL in febrile infants ≤60 days old is associated with IBIs. However, in the presence of normal PCT levels, no patients with leukopenia had IBIs. While this suggests leukopenia ≤2500 cells/µL is a risk factor for IBIs in non-critically ill young febrile infants only when PCT is unavailable or elevated, the overall low frequency of leukopenia in this cohort warrants caution in interpretation, with future validation required.