¹ Istituto di Chimica Clinica, Azienda Ospedaliera S. Maria della Misericordia, 33100 Udine, Italy
² Laboratorio di Patologia Clinica, Ospedale Civile, 30027 S. Donà di Piave (VE), Italy
³ Eurospital S.p.A., via Flavia 122, 34127 Trieste, Italy
⁴ Servizio di Immunologia e Microbiologia, Azienda Ospedaliera S. Maria degli Angeli, 33170 Pordenone, Italy
⁵ Laboratorio di Chimica Clinica e Microbiologia, Ospedale Civile, 33053 Latisana (UD), Italy

Correspondence to:
Dr E Tonutti, Istituto di Chimica Clinica, Azienda Ospedaliera S. Maria della Misericordia, 33100 Udine, Italy;
labanalisi{at}aoud.sanita.fvg.it Aims: Tissue transglutaminase (tTG) was recently identified as the major autoantigen in coeliac disease. The aim of this multicentre study was to evaluate the impact of a new immunoenzymatic assay for the detection of IgA anti-tGT antibodies.

Methods: Seventy four Italian and French clinical laboratories participated in this study; anti-tTG IgA with an enzyme linked immunosorbent assay (ELISA) method using guinea pig liver extract as the coating antigen, anti-endomysium IgA autoantibodies (EMA), and total serum IgA were determined in 7948 patients, 1162 of whom had coeliac disease (737 untreated cases and 425 on a gluten free diet). A proportion of the sera were then sent to a reference laboratory for anti-tTG retesting with an ELISA method using recombinant human tTG antigen.

Results: Seven thousand four hundred and fifty eight (93.8%) sera were EMA/antiguinea pig tTG concordant (positive or negative); 490 (6.2%) were non-concordant. The sensitivity of EMA and antiguinea pig tTG in the 737 untreated patients with coeliac disease was 92.1% and 94.8%, respectively, and the specificity was 99.8% and 99.2%, respectively. Retesting of the discordant sera showed that of the 162 sera classified as EMA negative/antiguinea pig tTG positive, only 49 were positive for human recombinant anti-tTG, and that 39 of these were also EMA positive. Furthermore, of the 36 sera classified as EMA positive/antiguinea pig tTG negative, only two were confirmed as EMA positive.

Conclusions: The antiguinea pig tTG assay is more sensitive but less specific than EMA, whereas the antihuman recombinant tTG assay is far more specific and just as sensitive as antiguinea pig tTG. Testing for EMA presents considerable interpretative problems and is difficult to standardise.

Keywords: anti-endomysium antibodies; antitissue transglutaminase antibodies; coeliac disease; immunoassay; recombinant human antigen

Abbreviations: AGA, antigliadin antibodies; ARA, antireticulin antibodies; AU, arbitrary units; CD, coeliac disease; CI, confidence interval; ELISA, enzyme linked immunosorbent assay; EMA, anti-endomysium antibodies; GFD, gluten free diet; IIF, indirect immunofluorescence; tTG, tissue transglutaminase; tTGgp; guinea pig liver tissue transglutaminase; tTGhr, human recombinant tissue transglutaminase

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