Persistent fetal hemoglobin in maternal circulation complicating the diagnosis of fetomaternal hemorrhage

BACKGROUND: Transplacental hemorrhage can be life threatening to a fetus and has important maternal treatment implications. In contrast, hereditary persistence of fetal hemoglobin is a condition that has little consequence. The Kleihauer-Betke test, which is routinely used to document transplacental hemorrhage, will be positive in either case. CASES: We report two cases in which maternal persistence of fetal hemoglobin was unknown and led to the erroneous diagnosis of fetomaternal hemorrhage. These cases highlight both the limitations of the Kleihauer-Betke test and the role of flow cytometry in diagnosing fetomaternal hemorrhage. CONCLUSION: The use of flow cytometry can clarify Kleihauer-Betke test results when there is known maternal persistence of fetal hemoglobin and can more precisely quantify a fetomaternal hemorrhage for accurate Rh immune globulin dosing.