Evaluation of six anti-gliadin antibody assays

Two in-house methods developed in gastroenterological laboratories for the detection and quantitation of IgG and IgA antibodies to gliadin (AGA) were compared with three commercially available ELISAs (gluten IgG/IgA EIA, Kabi Pharmacia, Sweden; alpha-Gliatest, Eurospital, Italy; AGA Orkit, Labodia, Switzerland) and one qualitative rapid assay (Gliastick, Eurospital, Italy). 67 acute, biopsy confirmed coeliac disease cases were compared with 54 biopsy confirmed disease controls. The result of anti-endomysium antibody (AEA) testing was available from all cases. The testing of 121 sera in different test systems permitted comparison of the range of concentration and sensitivity of the quantitative IgG and IgA anti-gliadin tests. Each test uses its own arbitrary calibration. To permit direct comparison of the different test ranges the values of the different positive reference sera were converted into Pharmacia arbitrary units (AU). The AGA and IgG tests ranged from 0 to a maximum of 157-430 AU and the maximum IgA test results from 81 to 855 AU. This illustrates the need for an internationally accepted standard. All three EIA kits met the performance claims of the manufacturers and were easy to use. Most results agreed with the clinical diagnosis when the sera were positive for anti-endomysium antibodies. However, AEA negative specimens showed a considerable incidence of positive AGA in non-coeliacs. The study emphasises the need to test for both AGA and AEA in order to reliably diagnose coeliac disease. The qualitative test showed a high degree of false positive results and could be used to monitor the dietary compliance of coeliac patients.