Tissue transglutaminase immunoglobulin isotypes in children with untreated and treated celiac disease

Objectives: Tissue transglutaminase (tTG) autoantibodies are serologic markers for celiac disease (CD). The aim was to determine the diagnostic sensitivity and specificity of different immunoglobulin isotypes against tTG. Methods: Immunoglobulin A (IgA)-tTG, IgG-tTG, and IgGl-tTG were measured in radioligand binding assays in 67 children with untreated and 89 children with treated CD and compared with 48 biopsy controls. IgM-tTG was measured in children with untreated CD and in biopsy controls. IgA endomysial autoantibodies (EMA) were analyzed in all children using an immunofluorescence method. Results: The sensitivity of IgA-tTG and IgG-tTG was 85.1% (57 of 67) and 83.6% (56 of 67), respectively, which both increased to 93.8% (45 of 48) in children diagnosed at age 2 years or older. Both had a specificity of 93.8% (45 of 48). IgA-EMA had a sensitivity of 80.6% (54 of 67) and a specificity of 91.7% (44 of 48). In treated CD, IgA-tTG and IgG-tTG were detected in 21.3% (19 of 89) and in 14.6% (13 of 89), respectively, despite negative EMA titers. IgGl-tTG was correlated to age (r = -0.47, P = 0.0005) and detected in 50.7% (34 of 67) with untreated CD compared with 11.2% (10 of 89) with treated CD and with 4.2% (2 of 48) of biopsy controls (P < 0.0001, respectively). IgM-tTG was detected in 1.5% (1 of 67) with untreated CD and in none of biopsy controls. Conclusion: IgA-tTG and IgG-tTG analyzed in radioligand binding assays are equivalent to IgA-EMA as screening tests for CD during childhood, but an intestinal biopsy is still the method of choice to establish the diagnosis. Although IgGl-tTG was more common at young age of diagnosis, both IgGl-tTG and IgM-tTG had low specificity and sensitivity and may not be useful as screening tests for CD.