When you wish to test or screen for coeliac, the test performed by the laboratory may vary according to local availability and patient characteristics. If the request is for “coeliac serology” the laboratory should:-
In young people and adults
- Test for total IgA and IgA tissue transglutaminase (tTG)
- If IgAtTG is weakly positive then test for IgA endomysial antibodies (IgA EMA)
- If there is a deficiency of IgA then IgG EMA, IgG deamidated gliandin peptide (IgG DGP) or IgG tTG may be tested
- Test for total IgA and IgA tTG first line
- Again if IgA is deficient use one or more of IgG EMA, IgG DGP or IgG tTG
It is vitally important that prior to testing, the person be instructed to eat gluten every day for 6 weeks. Failure to do this may lead to a false negative test.
A positive blood test should lead to referral to secondary care where endoscopy and duodenal biopsy are needed to confirm diagnosis. In the time lag between a positive test and endoscopy the person should be told to continue with gluten in the diet. The problems associated with removing gluten from the diet without specialist dietary advice are two fold. Firstly it adds to diagnostic confusion as biopsy and further serological testing may be negative and a poorly balanced diet may lead to further iron deficiency and weight gain.