Hematology and Immunology
Anemia and jaundice
Term infants reach a physiologic hemoglobin nadir of 9-11 g/dL at 8-12 weeks; preterm infants nadir at 7-9 g/dL at 4-6 weeks (anemia of prematurity). Transfuse based on symptoms, FiO2, and gestational age rather than a single threshold. Erythropoietin may reduce transfusions but is not routine for all.
Jaundice before 24 hours is pathologic. Hemolytic disease from Rh or ABO incompatibility produces a positive direct antiglobulin test, rising bilirubin, and anemia. Use hour-specific phototherapy thresholds by gestational age and risk factors; exchange transfusion for levels near the exchange line or signs of acute bilirubin encephalopathy. Give vitamin K 1 mg IM at birth to prevent vitamin K deficiency bleeding.
Platelets and immunity
Thrombocytopenia is a platelet count below 150,000/mcL. Neonatal alloimmune thrombocytopenia results from maternal anti-HPA-1a antibodies; treat with IVIG and HPA-matched platelets, not random donor platelets. Neonates have reduced opsonization and complement activity, increasing susceptibility to encapsulated organisms.
Worked example
An Rh-negative mother delivers a DAT-positive infant whose bilirubin rises 0.3 mg/dL/hour at 24 hours and hematocrit is 35%. Reasoning: hemolysis. Start intensive phototherapy, check hour-specific thresholds, consider IVIG if bilirubin is near exchange, and prepare for exchange if it continues to rise.
Traps
- Missing early jaundice as a sign of hemolysis or sepsis.
- Using phototherapy without supporting feeding and hydration.
- Giving random platelets in NAIT.