Platelet count and sepsis in very low birth weight neonates: is there an organism-specific response?

Thrombocytopenia is commonly observed in very low birth weight (VLBW) neonates with sepsis. Specific platelet responses to different infectious agents have not been extensively characterized. The objectives of this study were to examine platelet counts and platelet indices in preterm neonates with culture-proven sepsis to determine if there are organism-specific platelet responses.

We analyzed a cohort of all VLBW neonates (birthweight <1500 g) born over a 4-year period and admitted to a single level III neonatal intensive care unit (N = 943). Thrombocytopenia was defined as a platelet count <100,000/mm(3). Platelet count, nadir, duration of thrombocytopenia, and mean platelet volume (MPV) were examined during episodes of culture-proven sepsis. Analysis of variance, Kruskal-Wallis, Mann-Whitney U, and chi(2) tests were used to compare groups, and data are expressed as mean +/- standard deviation.

Sepsis was diagnosed in 154 (16%) of 943 patients in the study population. Of the sepsis episodes, 54% were associated with thrombocytopenia and 61% with an elevation in MPV. Infections were grouped by organism type: Gram-positive bacteria (117/154, 76%), Gram-negative bacteria (24/154, 16%), and fungi (13/154, 8%). When compared with patients with Gram-positive sepsis, those with Gram-negative or fungal sepsis had a significantly lower initial platelet count, a lower platelet nadir, a higher incidence of thrombocytopenia, and a greater duration of thrombocytopenia. The decrease in platelet count from baseline was also significantly less in the Gram-positive infections than in the fungal infections. Although there was an overall increase in MPV from baseline, there were no differences between groups.

In our population of VLBW infants, sepsis is frequently associated with thrombocytopenia and an elevation in MPV. However, fungal and Gram-negative pathogens are associated with a lower platelet count and more prolonged thrombocytopenia compared with Gram-positive pathogens. We conclude that common pathogens causing sepsis have different effects on platelet kinetics.