Serological and molecular characterisation of the most prevalent weak D variants in Croatian population.

INTRODUCTION: Existence of hundreds of RHD gene variants contributes to variable D antigen expression and inconsistencies in reporting the RHD results. The aim of the study was to determine the serological and molecular characteristics of the most prevalent RHD alleles encoding serologically weak D variants. MATERIAL AND METHODS: Blood donors (n = 145 924) were typed for D antigen using the direct serologic micromethod. Nonreactive samples were analysed in IAT method with the IgM/IgG anti-D monoclonal blend, and 0,2% (n = 263) confirmed weak D antigen expression. After genomic DNA extraction (Qiaqen, Germany), RHD genotyping was performed using in house reagents and PCR-SSP kits (Inno-Train, Germany). RESULTS: The prevalence of serologically weak D in blood donor population was 0.2% (n = 263). RHD genotyping confirmed weak D allele in 92.4% and partial D allele in 7.6%. The most common was weak D type 1 (49.7%) followed by weak D type 3 (24.7%) and type 2 (9.5%). Relatively high frequency was detected for weak D type 14 (4.6%) and type 64 (2.3%). In the category of partial D phenotypes, only DVI variant was found. Direct typing has shown great variability in the strength of reactions with different clones of anti-D reagents. CONCLUSION: Weak D type 1 is the most common weak D variant in Croatian blood donor population. The frequency of D variants and distribution of Rh phenotypes in our study was in concordance with other studies. It has been shown that serological methods and the combination of clones used, cannot distinguish variant D types, which justifies the use of molecular methods.

Prevalence of ABO and RhD blood group phenotypes in the Croatian population and in patients with severe COVID-19 in Croatia.

BACKGROUND: The aim of this study was to determine the distribution of ABO and RhD blood group phenotypes in the general population in the Republic of Croatia and among hospitalized patients with severe COVID-19. MATERIALS AND METHODS: Data on ABO and RhD blood groups of all blood donors in Croatia (who donated blood during the period 2015-2020) and patients and pregnant women tested at the Croatian Institute of Transfusion Medicine during the 2-year period, 2019-2020, were obtained from the e-Delphyn blood bank information system. A total of 614,673 results were analyzed in this group. The other group consisted of 780 COVID-19 patients hospitalized with severe COVID-19. Data are presented as total number and percentages and a comparison of proportions test was performed. RESULTS: The most frequent ABO phenotype in the general population is A (38%), followed by O (37%), B (18%) and AB (7%). RhD positive individuals accounted for 81% of the general population and RhD negative for the other 19%. Among COVID-19 patients, phenotype A was the most frequent (42%), followed by phenotypes O (32%), B (17%) and AB (9%). Thus blood group A was significantly more common among COVID-19 patients than among the general population, whereas blood group O was significantly less frequent. DISCUSSION: This study provides the first official results of the distribution of ABO and RhD blood group phenotypes in the general population in Croatia. Moreover, this study confirms other researchers' observations about the predominance of the A blood group phenotype among COVID-19 patients.