The Rhesus (Rh) blood group is the most polymorphic human blood group and it is clinically significant in transfusion medicine. Especially, D antigen is the most important and highly immunogenic antigen. Due to anti-D, it is the cause of the hemolytic disease of the newborn and transfusion reaction. About 0.1%-0.5% of Asian people are RhD-negative, whereas in the Thai population, the RhD-negative blood type only occurs in 0.3%. Approximately 10%-30% of RhD-negative in Eastern Asian people actually were D-elute (DEL) phenotype, the very weak D antigen that cannot be detected by indirect antiglobulin test (IAT). There are many reports about anti-D immunization in RhD-negative recipients through the transfusion of red blood cells from individuals with DEL phenotype. D-elute phenotype screening in Thai RhD-negative blood donors was studied to distinguish true RhD-negative from DEL phenotype. A total of 254 Thai serologically RhD-negative blood donors were tested for RhCE phenotypes and anti-D adsorption/elution test. In addition, RhC(+) samples were tested for RHD 1227A allele by SSP-PCR technique. The RhD-negative phenotype samples consisted of 131 ccee, 4 ccEe, 1 ccEE, 101 Ccee, 16 CCee, and 1 CcEe. The 42 Ccee and 8 CCee phenotype samples were typed as DEL phenotype and 96% of DEL samples were positive for RHD 1227A allele. The incidence of RhC(+) was 46.4%, and 48 of the 118 RhC(+) samples were positive for both anti-D adsorption/elution test and SSP-PCR technique for RHD 1227A allele. The sensitivity and specificity were 96% and 100%, respectively, for RHD 1227A detection as compared with the adsorption/elution test. In conclusion, RhC(+) phenotype can combine with anti-D adsorption/elution test and RHD 1227A allele SSP-PCR technique for distinguishing true RhD-negative from DEL phenotype. [ABSTRACT FROM AUTHOR]