 Guidelines recommend that a total serum IgA level is checked in parallel, as people with coeliac with IgA deficiency may be unable to produce the antibodies on which these tests depend ("false negative").In those people, IgG antibodies against transglutaminase (IgG-tTG) may be diagnostic.If all these antibodies are negative, then anti-DGP antibodies (antibodies against deamidated gliadin peptides) should be determined.