What serological tests should I order to confirm a diagnosis of Celiac disease in a patient with gastrointestinal symptoms?

To confirm a diagnosis of coeliac disease in a patient presenting with gastrointestinal symptoms, the following serological tests should be ordered:

• First-choice tests: Laboratories should test for total immunoglobulin A (IgA) and IgA tissue transglutaminase (tTG) as the first choice for both young people, adults, and children ¹.
• For weakly positive IgA tTG (young people and adults): If IgA tTG is weakly positive, IgA endomysial antibodies (EMA) should be used ¹.
• For IgA deficiency: If IgA is deficient (defined as total IgA less than 0.07 g per litre), consider using IgG EMA, IgG deamidated gliadin peptide (DGP), or IgG tTG ¹. A specific assay designed to measure total IgA levels should be used when testing for total IgA ¹.

Tests not to use for initial diagnosis in non-specialist settings: Do not use human leukocyte antigen (HLA) DQ2 (DQ2.2 and DQ2.5)/DQ8 testing in the initial diagnosis of coeliac disease in non-specialist settings ¹.

Important pre-test advice: For any serological test to be accurate, the patient must be eating a gluten-containing diet during the diagnostic process ¹. Patients should be advised to eat some gluten in more than one meal every day for at least six weeks before testing ¹. It is crucial that patients do not start a gluten-free diet until diagnosis is confirmed by a specialist, even if serological test results are positive ¹.