Differentiation of anti-D, -C, and -G: clinical relevance in alloimmunized pregnancies

The differentiation of anti-D, -C, and -G specificities is seldom considered clinically important in pretransfusion testing. However, distinguishing these antibody specificities in alloimmunized pregnancies may be essential. The clinical prognosis as well as Rh immune globulin prophylaxis depends on the accurate identification of these antibodies.

A pregnant woman, para 1 gravida 4, who had received Rh immune globulin at appropriate intervals during her previous pregnancies was reported to have anti-D (titer = 4) and anti-C (titer = 32). Differential adsorption and elution studies showed that the patient had anti-C and anti-G, but not anti-D. This case prompted retrospective examination of the sera from six other women with anti-D and anti-C who were referred to a high-risk pregnancy clinic. Of six pregnant women reported to have anti-D and anti-C; two had anti-D, -C, and -G; three had anti-D and -G, but not anti-C; and one had anti-C and -G, but not anti-D. This last is similar to the index case.

Cases of pregnant women with anti-C and -G, but not anti-D, are not infrequent. Studies to differentiate anti-D, -C, and -G should be performed on alloimmunized pregnant women presumptively identified as having anti-D and anti-C when the medical history (Rh immune globulin prophylactic therapy) and/or titer values (e.g., anti-C titer higher than anti-D titer) suggest that anti-D may not actually be present. Rh immune globulin has not failed in these patients, and they should receive this therapy during pregnancy to prevent immunization to D.