Aims: Tissue transglutaminase (tTG) is a major autoantigen recognised by IgA anti-endomysial antibodies (IgA EMA). Enzyme linked immunosorbent assays (ELISA) for IgA anti-tissue transglutaminase antibodies (IgA tTG) have therefore been developed as an alternative serological screening test to IgA EMA for coeliac disease (CD). The use of human tTG (h-tTG), as opposed to guinea pig liver tTG (gpl-tTG), in these assays has been reported to produce superior results. This study compared 13 commercial IgA tTG ELISA kits to ascertain their performance characteristics in the diagnosis of CD in patients with biopsy confirmed disease compared with controls. All patients and controls were adults aged 21 years or older.
Methods: Sera from the following groups of patients were tested in each kit: (1) 49 patients with CD confirmed on small bowel biopsies (all IgA EMA positive); (2) 34 patients with small bowel biopsies that were not consistent with CD; and (3) 30 patients with biopsy confirmed inflammatory bowel disease. All controls were negative for IgA EMA and were not IgA deficient. Sensitivities and specificities were determined using both the manufacturers' recommended cut off points and receiver operating characteristic (ROC) analysis derived decision thresholds. The area under the curve (AUC) for each ROC plot was also calculated and compared between kits.
Results: In general, the h-tTG based IgA tTG ELISA kits demonstrated superior performance (especially specificity) compared with the gpl-tTG based kits, although 100% sensitivity and specificity (comparable to the IgA EMA assay) was obtained in only one recombinant h-tTG based kit.
Conclusions: The use of h-tTG in IgA tTG ELISA kits is generally, but not universally, associated with superior performance. Factors other than antigen source are important in determining kit performance.