Celiac.com 03/12/2009 - The latest antihuman tissue transglutaminase (tTG) IgA tests are reported to spot celiac disease with nearly 100% sensitivity and specificity. Also, a new generation of deamidated gliadin peptide (Î±-DGP) antibody tests is alleged to have sensitivity levels on par with the tTG IgA tests. However, in actual practice, sensitivity and specificity for these tests are often lower than claimed for trial conditions.
A team of Columbia University researchers recently evaluated sensitivities and specificities of four commercial IgA tTG kits, along with three commercial deamidated gliadin peptide (Î±-DGP) kits. The team evaluated the results for four tTG IgA assays: A—Inova (Hu red blood cell); B—Binding site (rHu Ag); C—Eurospital (rHu Ag), D—Immco (rHu Ag) and three Inova Î±-DGP assays, E—Î±-DGP-IgA, F—Î±-DGP-IgG, and G—Î±-DGP-IgA+G.
The team used blood samples from four different groups of celiac disease patients and controls: Group 1 consisting of 28 patients with active celiac disease; Group 2 consisting of 54 celiac patients following a gluten-free diet; Group 3 consisting of 40 healthy controls; Group 4 consisting of 57 disease controls—17 with Crohn's disease, and 40 with chronic hepatitis. In each case, the researchers used the manufacturer's own cut-off values. They found that sensitivities and specificities of different kits ranged from 71.4% to 96.4% and 87.5% to 100%, respectively.
Compared with disease controls, sensitivity for Group 1 stayed the same, while specificity fell. All tests showed higher sensitivities for higher patient villous atrophy. The study showed that overall sensitivity was 90% or less, which is below figures reported in the literature.
Recombinant and red blood cell antigen-based tTG assays performed similarly, while the Î±-DGP tests showed lower values. The bottom line was that a number of factors can influence the sensitivity and specificity for these test, and that doctors should keep these facts in mind when evaluating patients.
Journal of Clinical Gastroenterology: Volume 43 (3) March 2009, pp 225-232