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 (<0.05 g/L), 21 patients with low IgA levels (<0.16 g/L) were tested by means of an ELISA method for the detection of anti-tissue transglutaminase antibodies (Eu-tTG®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 <0.2 AU/ml Low serum IgA values: 19/21 sera gave TGA values below 1 AU/ml All the normal serum IgA sera gave values above 1 AU/ml. The CD patients had values of 14.1 and 14.6 AU/ml respectively.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.