Identification and quantification of anti-D, -C and -G in alloimmunized pregnant women

Our objectives were to investigate possible overestimation of maternal anti-D due to co-existing anti-C and/or anti-G, and to confirm the presence of anti-D in plasma presumed to contain anti-D+C. We investigated 96 samples (from 22 antenatal patients and 74 blood donors) initially identified as containing anti-D+C using routine investigation procedures. Anti-D quantification was performed using an Astoria Pacific International 300 (API 300) continuous flow analyser with R1R1 and R2R2 reagent red cells. Where possible, samples were tested manually using a rare D+, C-, G- cell, to confirm the presence of anti-D. Fifty-two of 96 samples (11/22 antenatal patients and 41/74 blood donors) gave >50% higher anti-D quantification results with R1R1 cells than with R2R2 cells. Anti-D was not detected using manual techniques in 16 of 73 samples tested (10/22 antenatal patients and 6/51 blood donors). Anti-D quantification using R1R1 reagent red cells may cause inaccurate estimation of anti-D levels, when anti-C and/or anti-G are present. Indeed, a significant number of cases, where apparent anti-D+C is identified, may contain only anti-C+G and lack an anti-D component. This may in turn lead to a failure to administer prophylactic anti-D immunoglobulin to RhD negative patients in cases where anti-D is not present, putting these patients at risk from immunization with possible consequences to future pregnancies.