IgA and IgG Antitransglutaminase 2 Antibodies in the Diagnosis of Celiac Disease

Screening for celiac disease (CD) dramatically improved when techniques able to measure blood autoantibodies against tissue transglutaminase 2 (TTG) were developed. Although typically increased in CD, these antibodies are not pathognomonic since they are also detected in several other autoimmune processes. IgA deficiency among celiac patients is more frequent than in general population (up to 25% vs 1-3%). This led to develop kits able to measure IgG-TTG, which until today represent a helpful diagnostic tool during diagnosis of CD in IgA deficient individuals. Today, commercial kits measuring IgG- TTG (and other) antibodies are widely available, are frequently used and create confusion in diagnosing CD in IgA-sufficient individuals. This is attributed to the fact that sensitivity and specificity of IgG-TTG is lower when applied to IgA-sufficient persons, and also because IgG-TTG is detected in several autoimmune disorders, with variable frequency and isotypes depending on the condition. Evidence analyzed indicate that to date available data: i) is insufficient to understand the difference of classes and subclasses detected in CD and other autoimmune conditions; ii) does not support the use of IgG-TTG for diagnosing CD in IgA-sufficient individuals and therefore iii) IgG should not be used in the routine diagnostic process of CD.