Authors:
D. Pritchard (Cardiff, GB)
M. Rees (GB)
C. Darke (Pontyclun, GB)
UK NEQAS for H&I’s Scheme 4A2 assesses participant’s ability to correctly determine HLA alleles to the 2nd field resolution. As a minimum requirement, participants must resolve all ambiguities resulting from polymorphisms within exon 2 and 3 for HLA class I loci, and exon 2 for class II loci. Ten blood samples are distributed per year and participants can report 2nd field results for any combination of HLA loci. Alleles reported by at least 75% of labs are taken as the consensus HLA type. Results from 2013-2016 were analysed. 69 labs tested between 5-40 samples, resulting in 23,928 allele assignments to the 2nd field. The most commonly typed loci were HLA-DRB1 (n=4,080) followed by DQB1 (4,033), HLA-A (3,547), HLA-B (3,682), HLA-C (3,539), DPB1 (2,438), DQA1 (1,299), DRB3/4/5 (1,125) and DPA1 (185). A total of 163/23,928 alleles were incorrect; thus the overall error rate was 0.68%. The highest error rate was for DRB3/4/5 (2.13%, n=24), followed by HLA-C (1.10%, n=39), DQB1 (0.69%, n=28), DRB1 (0.66%, n=27), DQA1 (0.62%, n=8), DPB1 (0.57%, n=14), HLA-A (0.34%, n=12), HLA-B (0.30%, n=11); with no errors for DPA1. 61/163 errors involved multiple errors (2-6 incorrect alleles) on the same sample. 58.0% (40/69) of labs reported an incorrect allele during the 4 years; 15 labs had 1 allele error, 25 had multiple incorrect alleles. Many errors (49.1%, n=80) were due to reports not meeting the minimum typing requirements, i.e. reports of allele strings with alleles differing in exon 2 (class II) and exons 2 and 3 (class I). 59 (36.2%) errors were due to reports with the incorrect 2nd field HLA (e.g. B*07:01, not B*07:02). 14 errors (8.6%) were due to missed alleles and 10 errors (6.1%) were at the 1st field (e.g. C*06:02 not C*07:02).
It is important that laboratories are able to perform accurate HLA typing to the 2nd field level, especially in support of HSC transplantation. The low overall error rate is encouraging, however further work is required to eliminate errors that could impact on patient care.