P154 The quest for resolving a mystery

Introduction Accurate HLA typing for patients in need of allogeneic stem cell transplant is crucial for finding a matched donor & improving graft outcome by preventing graft-versus-host disease. We report here a case of mystery while HLA typing for a patient. Method We routinely perform Luminex SSO typing of HLA-class I & II loci for the initial sample first, followed by sequence-based typing (SBT) on the CT sample per SSO results for appropriate selection of SBT primers. The case Day 1, two peripheral blood (PB) (1 for initial, 1 for CT) collected 90 min apart by 2 phlebotomists were received. SSO typing was obtained successfully from 1st PB. Day 2, buccal swabs were received with an indication of circulating blasts in patient’s blood. SBT were performed on the buccal DNA per SSO results on 1st PB, typing was obtained for only those with locus primers but failed with group primers. Moreover, the SBT results didn’t match with those of the 1st PB. We SSO-typed the 2nd PB (CT sample), the typing matched with those of the 1st PB but not the buccal. Day 3, a PB sample of the patient’s son was received, typing results showed one haplotype match with the patient’s buccal results but not with any of the 2 PB results. A sample switch? The first two PB were re-extracted, typing results matched with those of previously obtained, suggesting that no sample switch had occurred in the lab. Is it possible a sample switch at collection sites? It seems very unlikely per the collection procedures. Where is the problem? Medical history was reviewed and showed that the patient had a history of low WBC counts and had multiple granulocyte infusions prior to HLA sample collection including one in less than 22 h to the 1st PB to HLA. Typing of the granulocyte donor were conducted and results were concordant with those of the 2 PB. Retyping of the 1st PB by SBT using appropriate group primers confirmed a low level of patient’s DNA that was masked by the much higher levels of granulocyte donor’s DNA. Another buccal sample from 3 weeks later showed concordance with the first buccal typing. Conclusion It is very important for HLA laboratory to know the transfusion history and previous transplant history in order to apply appropriate test procedures. It’d be imperative and good practice to recommend to testing buccal swab sample for every patient in need of allogeneic stem cell transplant.