# Harmonisation of the HLA tests for the diagnosis of coeliac disease: experiences from the Czech external proficiency testing program

## TL;DR

This paper discusses efforts to improve the consistency and accuracy of HLA testing for diagnosing coeliac disease in the Czech Republic.

## Contribution

A new 2023 classification system for HLA genotypes in coeliac disease diagnosis is introduced and evaluated.

## Key findings

- Annual proficiency testing revealed ongoing issues with HLA allele detection and interpretation.
- A three-category HLA genotype classification system was adopted to guide clinical decision-making.
- Workshops and updated recommendations have improved test quality, though further improvements are needed.

## Abstract

Coeliac disease (CD) is an autoimmune disorder caused by the ingestion of gluten-containing grains. One of the prerequisites for the development of the disease is the presence of specific combinations of HLA alleles at the DQA1 and DQB1 loci. The HLA test is a supportive diagnostic test. In the Czech Republic, approximately 3,500 HLA tests for CD diagnosis are performed annually in almost three dozen laboratories. The HLA Department of the Institute of Haematology and Blood Transfusion in Prague has been offering the EPT “Detection of HLA Alleles Associated with Diseases” for more than 10 years. The results are evaluated in terms of the correct determination of predisposing alleles/allelic groups and clinical interpretation. Every year, we notice some problems with the detection of CD-associated alleles and the interpretation of results. Annual workshops are part of this EPT, and they also include recommendations for the interpretation of results. This interpretation is evolving based on the current knowledge in the field. The current recommendation for interpretation was adopted in 2023, dividing HLA-DQA1/DQB1 genotypes into three categories: 1) detected HLA genotype is associated with predisposition to coeliac disease; 2) coeliac disease could not be excluded based on the detected HLA genotype; 3) coeliac disease could be excluded with high probability based on the detected HLA genotype. The quality of examination is increasing but still needs improvement. Correct results and accurate interpretation can inform clinicians’ decisions about the diagnosis of coeliac disease in appropriate patients.