Screening for coeliac disease using anti-tissue transglutaminase antibody assays, and prevalence of the disease in an Australian community

Objectives: To determine (i) the prevalence of positive results of anti-tissue transglutaminase (anti-tTG) antibody assays and coeliac disease (CD) in a rural Australian community; and (ii) whether confirmatory testing of a positive assay result with an alternative anti-tTG assay improved the positive predictive value of the test in population screening for CD. Design: Retrospective analysis in December 2004 of stored serum samples taken in 1994-1995 from 3011 subjects in the Busselton Health Study follow-up. Assays for IgA and 19G anti-tTG antibodies were performed, and positive or equivocal samples were retested with a different commercial anti-tTG assay. Available subjects with one or more positive assay results were interviewed, had serum collected for repeat anti-tTG assays and for HLA-DQ2 and HLA-DQ8 haplotyping and, if appropriate, gastroscopy and duodenal biopsy were performed. In unavailable subjects, HLA-DQ2 and -DQ8 haplotyping was performed on stored sera. Total serum IgA levels were assessed in subjects with initially negative assay results. Main outcome measure: Prevalence of anti-tTG positivity and biopsy-proven CD. Results: In 47 of 3011 serum samples (1.56%), at least one anti-tTG assay gave positive results: 31 of the subjects who provided these sera were available for clinical review, and 21 were able to have a gastroscopy. Seventeen subjects (0.56%) were diagnosed with definite CD (14 were confirmed at gastroscopy, and three unavailable subjects had three positive results of anti-tTG assays and an HLA haplotype consistent with CD); in a further 12 unavailable subjects, CD status was considered equivocal, with one or more positive anti-tTG assay results and an HLA haplotype consistent with CD. If these subjects were regarded as having CD, the prevalence of CD would be 0.96%. The positive predictive value when all three anti-tTG assays gave positive results was 94%, but fell to 45.2% with only one positive result. Conclusions: The prevalence of anti-tTG antibodies in this population is 1.56%; the prevalence of CD is at least 0.56%. The utility of a single, positive result of an anti-tTG assay in screening for CD in the community is poor, and repeat and/or collateral assessment with different assays may decrease the need for gastroscopy and distal duodenal biopsy.