Study design. (A) Samples: number of DNA samples provided by the 7 blood services (NHSBT, SANQUIN, NYBC, ARCLB, CBS, FRCBS, SANBS). (B) Array content: bar plot indicating the number of probes per category in the transfusion module. HLA, HEA, HPA, and HNA. (C) Genotyping: 6946 identical DNA samples were genotyped with the UBDT_PC1 Transfusion Array at Sanquin and NYBC, with 3938 of these samples also genotyped using the UKBB_v2.2 GWAS array by NHSBT. (D) QC: Heat map gives the reason for, and number of, samples failing QC for the 3 genotyping laboratories. Venn diagrams show overlap in samples that failed Axiom BP QC, gender-vs-sex discordance (sex discordant), and evidence of contamination (contamination). (E) Venn diagram showing the overlap in samples passing QC. (F) Ancestry: (left) bar plot showing genetically inferred ancestry of samples typed successfully by Sanquin and NYBC (6679 samples). EUR, AFR, AMR, SAS, EAS, OTH are shown. Right: heat map showing concordance between the ancestry inferred from the Sanquin and NYBC genotyping results, respectively. AFR, African; AMR, Admixed American; ARCLB, Australian Red Cross Lifeblood; Axiom BP, Axiom Best Practices; CBS, Canadian Blood Services; EAS, East Asian; EUR, European; FRCBS, Finnish Red Cross Blood Service; OTH, Other; SANBS, South African National Blood Service; SANQUIN, Sanquin Blood Supply Foundation; SAS, South Asian.