EVIDENCE SUMMARY
A 2013 Belgian prospective study of 104 non-IgA–deficient adults and children diagnosed with celiac disease and 537 adults and children without celiac disease evaluated the accuracy of 4 manufacturers’ serologic tests for IgA anti-tTG.1 All patients underwent serologic testing followed by a diagnostic biopsy. A Marsh type 3 or greater lesion on duodenal biopsy was considered diagnostic for celiac disease.
Anti-tTG levels greater than 10 times the manufacturer-recommended level for a positive test (cut-off) were associated with a likelihood ratio of 111 to 294 (depending on the manufacturer) of positive biopsy. Post-test probabilities were calculated based on various pretest probabilities using an anti-tTG level of greater than 10 times the cut-off (TABLE1).
Investigators also obtained IgG anti-DGP levels from 2 of the manufacturers.1 Likelihood ratios increased along with antibody levels. Ratios of 80 and 400, depending on the manufacturer, were found at IgG anti-DGP levels 10-fold greater than the cut-off. Pre- and post-test probabilities weren’t calculated.
Positive predictive value rises with antibody levels
A 2013 retrospective study evaluated the European Society for Pediatric Gastroenterology, Hepatology, and Nutrition’s recommendation to forego intestinal biopsy in non-IgA–deficient, symptomatic children and adolescents with positive IgA anti-tTG levels greater than 10 times the cut-off value, positive EMA, and positive HLA-DQ2 or HLA-DQ8.2
Overall, 153 symptomatic patients referred to the gastroenterology unit met these criteria. The age range was 9 months to 14.6 years (mean 4 years). All but 3 of the patients had Marsh 2 or greater lesions with biopsy-confirmed diagnoses of celiac disease. The remaining 3 developed biopsy-positive celiac disease on follow-up. The positive predictive value of combined serologic testing in this small selected patient population was 100%.