A study on Rh incompatibility and frequency of weak D among blood donors and patients at a tertiary care referral teaching hospital in Tirupati, Andhra Pradesh

Background: Rh D antigen is the next most important after ABO antigens in the field of transfusion medicine. Weak D refers to reduced expression of D antigen on the red blood cell that requires an extended testing with indirect antiglobulin test (IAT) to get detected. Clinical importance of weak D arises when labelling the donor and patient, as the donor is labelled as D positive, patient as D negative. Methods: In our center all blood donor and patient samples are tested for ABO and Rh D by conventional tube technique using two anti-D reagents; anti-D immunoglobulin M (IgM) monoclonal and a blend of anti-D IgM and immunoglobulin G (IgG). The blood samples which were negative for agglutination by immediate spin method were further tested for weak-D using IgG anti-D in the IAT phase with low ionic strength solution (LISS)/Coombs’gel card. Results: A total of 46,654 blood samples were tested (22,326 donors and 24,328 patients) during the period January 2012 to August 2014. Among these 43,771 (93.82%) were Rh D positive and remaining 2,883 (6.18%) were Rh-D negative. A total of 30 individuals (16 donors and 14 patients) were weak D positive constituting 1.04% of Rh-D negatives and 0.06% of total individuals screened. Conclusions: This study shows the prevalence of weak D antigen in our population who are representative of Rayalaseema region of Andhra Pradesh. It also stresses the need to identify individuals with variant D (rather than weak or partial D) and to inform them about their status as donor and recipient of blood/organ.