Evaluation of methods for detection and quantitation of fetal cells and their effect on RhIgG usage

A 1980 College of American Pathologists Immunohematology Survey included two erythrocyte suspensions, one with and one without fetal cells, designed to evaluate methods for detecting and quantitating fetomaternal hemorrhage in Rh immune globulin candidates. Data from a supplementary questionnaire regarding Rh immune globulin administration during 1979 were compared by methods used. The most commonly used screening test was the microscopic Du. With this test, 12.2% of nearly 2,000 laboratories obtained a false negative result on an unknown which contained approximately 0.6% Rh positive erythrocytes. On this 100% adult cell suspension two-thirds of laboratories using acid elution technics reported the presence of fetal cells. Laboratories using Fetaldex to screen for and quantitate fetomaternal hemorrhage had the highest rate of false positives on this unknown and reported higher rates of multiple vial Rh immune globulin administration when compared to institutions using other acid elution procedures. The second unknown in this survey contained approximately 0.4% fetal cells. About one third of laboratories, using each of four acid elution technics, reported values less than one half to more than twice this amount. The number of false positive and false negative results and the wide scatter of quantitation amounts reported for these two unknowns suggest that better methods are needed for screening and quantitating fetomaternal hemorrhage.