Inflammation, anemia, and vitamin D levels associate with infant thrombocytosis risk.

BACKGROUND

Thrombocytosis (>500 × 103 platelets/μL blood) occurs in infants due to infection, inflammation, and/or anemia. Thrombocytosis and extreme thrombocytosis (EXT, >1000 × 103 platelets/μL blood) can present diagnostic dilemmas, sometimes prompting invasive testing and anticoagulation therapy. We previously identified heightened thrombocytosis rates in hospitalized infants versus older children, but this population largely excluded extremely preterm infants at increased risk for infections and anemia-factors that promote thrombocytosis.

OBJECTIVES

To define thrombocytosis and EXT rates, etiologies, and sequelae among infants hospitalized in tertiary neonatal intensive care units (NICUs) to assist clinical decision making and determine factors that associate with thrombocytosis risk in preterm and full-term patients.

METHODS

Retrospective analysis of thrombocytosis and EXT cases among 20,818 infants hospitalized in 2 tertiary NICUs from 2011 to 2023, compared to 10,323 patients hospitalized at a quaternary NICU.

RESULTS

Our results revealed thrombocytosis in 3% of all patients (8% of preterm infants). Both estimates were significantly lower than the incidence of thrombocytosis in quaternary NICU patients (20%). EXT was also reduced in our tertiary unit (0.08% vs 0.5% in quaternary NICU). Thrombocytosis was associated with leukocytosis and relative anemia, but not with thrombotic or bleeding complications. Thyroid hormone, liver-derived thrombopoietin, and vitamin D deficiency can drive thrombocytosis in adults. Vitamin D level, but not thyroid hormone or liver function, was inversely correlated with platelet count among infants with thrombocytosis.

CONCLUSIONS

Inflammation, anemia, and vitamin D level correlate with infant thrombocytosis and EXT. Liver and thyroid immaturity do not appear to impact thrombocytosis risk. There were no thrombotic complications associated with EXT. These results provide important context for interpreting the origins and appropriate clinical responses to thrombocytosis in preterm infants.