Neonatal hemolytic anemia due to pyknocytosis

A newborn boy was referred to our hospital because of hemolytic anemia and severe hyperbilirubinemia. Extensive investigations aimed at determining the cause of hemolysis was initiated at the time of admission and 3 months after blood transfusion. Notably, no intrinsic erythrocyte abnormalities could be detected. The only possible cause explaining the progressive anemia and unconjugated hyperbilirubinemia was the finding of pyknocytes, severely distorted erythrocytes, on the blood film at hospital admission. We propose a role for an increased free fraction of plasma unconjugated bilirubin in the formation of pyknocytes through bilirubin membrane toxicity with subsequent anemia and progressive hyperbilirubinemia. Conclusion: Pyknocytosis is a transitory erythrocyte-related condition which can result in severe anemia and hyperbilirubinemia. Recognition of pyknocytes by microscopic analysis of a blood film is essential for a correct diagnosis. Treatment consists of correction of the anemia by top-up blood transfusion and light therapy to prevent toxic bilirubin buildup. High levels of free unconjugated bilirubin could be the underlying cause for the formation of pyknocytes.