Objective estimation of the HLA typing quality of the donor registry could be deduced from the analysis of confirmatory typing results. We tested this approach in the Czech National Marrow Donors Registry. CT results information has been continuously collected separately for HLA-AB (serology) and DRB1 (DNA) during period of 1998- 2005. Altogether 758 results were analysed for HLA-A,B and 1107 for DRB1. Serological HLA-A,B phenotypes were confirmed in 704 (92.9 %) donors with the 2972/3032 (98 %) correctly serologically assigned HLA-A,B antigens. In 26/54 (48%) of incorrectly typed, the discrepancies were caused by serologically missed antigens. In this group the less frequent or rare antigens predominates (14/27 discrepancies in 26 donors). In the misassigned and overassigned antigen group a prevalence of CREG-type errors was reported (28/33 discrepancies in 31 donors), with a majority being wrongly assigned splits (19/28 CREG errors). In totally, 16/54 (30 %) of unconfirmed results were related to A19 group mistyping. The DRB1 accuracy was excellent; only 8/1107 (0.7%) donors were unconfirmed. Discrepancy rate was insignificantly higher for donors recruited during 1993-98 than for donors recruited later (59 vs. 41 %, p=0,21). The system represents a simple tool allowing determination of the quality of HLA-A, -B serological, as well as DRB1* DNA typing of a national registry, and complements classical QC programmes. The transition to DNAbased typing of Class I at recruitment will solve the problem of errors inherent in serology.

        Key words: confirmatory typing, HLA typing, quality control, serology, stem cell registry, typing discrepancies, DNA analysis