Selective hemolysis of adult red blood cells: An aid to prenatal diagnosis of hemoglobinopathies

Prenatal detection of hemoglobinopathies is difficult if placental blood samples are contaminated by maternal cells. Since fetal red cells contain less carbonic anhydrase than adult erythrocytes, adult cells can be preferentially hemolyzed in NH₄CI-NH₄HCO₃ acetazolamide (the Orskov-Jacobs-Stewart reaction). In the conditions used in our experiments, 50% of the adult cells were hemolyzed in 1.2 min, while this occurred at 12.3 min with fetal cells. When 2.5% fetal cells were mixed with adult red blood cells, an average of 2.3% of the cells was recovered after 3-6 min of Orskov-Jacobs-Stewart reaction. Analysis of cell size with the Coulter Channelyzer indicated that small adult cells had been hemolyzed and only large fetal cells remained. When the cells had been labeled with ³H-leucine, approximately 36% of the radioactive protein was recovered. Enrichment for fetal compared to adult β chain radioactivity was 100- to almost 1000-fold in double-label experiments. In normal fetuses, the β/γ synthetic ratio is 0.07-0.11. In ten studies of mixtures of 2.5% fetal blood in adult blood, mean β/γ was 0.482 before and 0.082 after Orskov-Jacobs-Stewart hemolysis. The ratio was 0.091 in pure fetal blood. Fetal phenotypes of sickle trait, β-thalassemia trait, and β-thalassemia major were also detected following Orskov-Jacobs-Stewart hemolysis. Thus this hemolytic procedure provides pure fetal blood from samples with only 2.5% fetal cells and enables the appropriate diagnoses to be made.