IgG class anti-DGP antibodies may be useful in people with IgA deficiency. In children younger than two years, anti-DGP antibodies perform better than anti-endomysial and anti-transglutaminase antibodies tests.Because of the major implications of a diagnosis of coeliac disease, professional guidelines recommend that a positive blood test is still followed by an endoscopy/gastroscopy and biopsy. A negative serology test may still be followed by a recommendation for endoscopy and duodenal biopsy if clinical suspicion remains high.Historically three other antibodies were measured: anti-reticulin (ARA), anti-gliadin (AGA) and anti-endomysial (EMA) antibodies. ARA testing, however, is not accurate enough for routine diagnostic use. Serology may be unreliable in young children, with anti-gliadin performing somewhat better than other tests in children under five. Serology tests are based on indirect immunofluorescence (reticulin, gliadin and endomysium) or ELISA (gliadin or tissue transglutaminase, tTG).Other antibodies such as anti–Saccharomyces cerevisiae antibodies occur in some people with coeliac disease but also occur in other autoimmune disorders and about 5% of those who donate blood.Antibody testing may be combined with HLA testing if the diagnosis is unclear. TGA and EMA testing are the most sensitive serum antibody tests, but as a negative HLA-DQ type excludes the diagnosis of coeliac disease, testing also for HLA-DQ2 or DQ8 maximises sensitivity and negative predictive values.
A small proportion have abnormal coagulation because of vitamin K deficiency and are at a slight risk of abnormal bleeding. Miscellaneous
Coeliac disease has been linked with many conditions. In many cases, it is unclear whether the gluten-induced bowel disease is a causative factor or whether these conditions share a common predisposition. IgA deficiency is present in 2.3% of people with coeliac disease, and is itself associated with a tenfold increased risk of coeliac disease. Other features of this condition are an increased risk of infections and autoimmune disease. Dermatitis herpetiformis, an itchy cutaneous condition that has been linked to a transglutaminase enzyme in the skin, features small-bowel changes identical to those in coeliac disease and may respond to gluten withdrawal even if no gastrointestinal symptoms are present. Growth failure and/or pubertal delay in later childhood can occur even without obvious bowel symptoms or severe malnutrition. Evaluation of growth failure often includes coeliac screening. Pregnancy complications can occur if coeliac disease is pre-existing or later acquired, with significant outcomes including miscarriage, intrauterine growth restriction, low birthweight and preterm birth. Hyposplenism (a small and underactive spleen) occurs in about a third of cases and may predispose to infection given the role of the spleen in protecting against harmful bacteria. Abnormal liver function tests (randomly detected on blood tests) may be seen.Coeliac disease is associated with several other medical conditions, many of which are autoimmune disorders: diabetes mellitus type 1, hypothyroidism, primary biliary cholangitis, microscopic colitis, gluten ataxia, psoriasis, vitiligo, autoimmune hepatitis, primary sclerosing cholangitis, and more.