The presence of fetal cells in maternal circulation can be determined with a Kleihauer-Betke test. Fetal cells contain fetal hemoglobin, HbF, which is resistant to acid elution. Adult Hb, which contains little to no HbF, is not resistant, and will be lost from the cell. After incubation in acid solution, the fetal cells will stain brightly with the pink dye, but adult cells will be ghostly pale. The test can be used to determine if placental trauma has occurred, how much Rh immune globulin should be given to an Rh negative mother, and even to test children with sickle cell disease for a protective pattern of persistent HbF. The image shows about 10% fetal cells.
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