CD79A and selective IgA deficiency disease: Current guidelines by the National Institute for Health and Care Excellence (NICE) recommend testing for total immunoglobulin A (IgA) and IgA tissue transglutaminase (tTG) as a first choice in both adults and children.16 In case of IgA deficiency, IgG tTG, IgG endomysial antibody (EMA) or IgG deamidated gliadin peptide (DGP) can be measured.