Hereditary persistence of fetal hemoglobin presenting as fetal-maternal hemorrhage.

This report describes a case of hereditary persistence of fetal hemoglobin (HPFH) presenting initially as a marginal placental abruption in a primiparous woman at 27 weeks gestation. Persistent but erratic elevation of percent hemoglobin F positive cells, as determined by a modified Kleihauer-Betke method, complicated the remainder of her pregnancy. The clinical impression of placental abruption with possible extension could not be documented by ultrasound or examination of the placenta at delivery. Hemoglobin electrophoresis followed by quantitative fetal hemoglobin first suggested the diagnosis of HPFH, which was confirmed seven months postpartum. Furthermore, the magnitude of percent positive F-cells could be profoundly altered by subtle changes in pH of the acid elution reagent. This case demonstrates that positive acid elution tests for maternal-fetal transfusion may be caused by elevated maternal hemoglobin F. Erratic results, elevated quantitative hemoglobin-F and sensitivity to reagent pH should alert the pathologist to this diagnosis and alter clinical management.