Duffy and Kidd Genotyping Facilitates Pretransfusion Testing in Patients Undergoing Long-Term Transfusion Therapy

OBJECTIVE: Conventional serologic typing of red blood cell systems other than ABO and RhD can be inaccurate and difficult to interpret in patients who have recently undergone blood transfusion. While molecular-based assays are not used routinely, the usefulness of genotyping was investigated in order to determine patients who may benefit from this procedure. METHODS: Blood samples were taken from 101 patients with haemato-oncological, chronic renal, or gastroenterological diseases and from 50 donor controls; the samples were tested for Fya and Fyb by applying serologic and genetic methods. All patients had received 3 or more units of RBCs during the last 3 months. An average of 6.1 RBC units were transfused per patient. The average length of time from transfusion until blood sampling was 24.4 days. The haemagglutination test was applied for serological analysis, and the restriction length polymorphism assay was used for genotyping. RESULTS: In total, 33 (32.7%) patients showed positive reactions with anti-Fya or anti-Fyb while being negative genetically. False-positive Fya results were found in 23 samples, and false-positive Fyb in 10 specimens. During the last 3 months, significantly more RBC units were transfused to patients with discrepant results than to those with accurate phenotyping/genotyping results: median of 5 (mean±SE: 6.85±0.69) versus median of 4 (mean: 5.71±0.51), respectively (p=0.025). The median length of time after the last transfusion was 25 days (mean: 28.72±2.23 days) in the group with accurate phenotyping/genotyping results versus a median of 14 days (mean: 15.52±1.95 days) in the group with discrepant results (p=0.001). Phenotypes and genotypes coincided in all donor samples. CONCLUSION: Genotyping assays for the Duffy system should be considered if the patient underwent blood transfusion less than 3 or 4 weeks before the sample collection. If the time frame from RBC transfusion exceeds 6 weeks, Duffy phenotyping can provide accurate results