Anti-tissue transglutaminase antibodies in IgA deficient sera: might a proper cut-off value be of help in avoiding total serum IgA testing?

Abstract Background: The introduction of an ELISA for antibodies to tissue transglutaminase has opened an new era in the diagnosis of coeliac disease by offering a simple, reliable and observer non-dependent method for the identification of coeliac patients. Despite its high sensitivity and specificity, false negative results can be achieved if a total serum IgA deficiency occurs. IgA deficient sera need to be tested to assess the level of total serum IgA to exclude possible false negative results. Aim: The aim of this study was to evaluate whether it is possible to define a cut-off value for an anti tissue transglutaminase ELISA which could indicate total IgA deficiency. In such patients further IgA isotype testing would only be necessary. Methods: 75 sera from patients with total IgA serum deficiency ( ® IgA, Eurospital, Italy). Five patients (including 2 subjects affected by coeliac disease) with normal IgA values (>0.2 g/L) were used as controls. Results: Total IgA deficient sera: 75/75 sera gave anti TGA values Conclusion: These results are preliminary data and need to be confirmed by means of additional data. However, total serum IgA deficient sera did not show Eu-tTG ® IgA values above 1 AU/ml. The use of a cut-off value at 1 AU/ml might be useful in deciding whether to perform total IgA serum determinations in those patients whose serum TGA values are lower than 1 AU/ml.