How to test
Diagnosis in adults
Coeliac disease in adults is diagnosed by serological testing and endoscopic intestinal biopsy. People with coeliac disease produce tissue transglutaminase antibodies (tTGA) and endomysial antibodies (EMA) when gluten is ingested.
When requesting tests for adults, NICE recommends:
- test for total immunological immunoglobin A (IgA) and IgA tissue transglutaminase as a first choice test
- use IgA endomysial antibodies (EMA) if IgA tTG is weakly positive
- consider using IgG EMA, IgG deamidated gliadin peptide (DGP) or IgG tTG in cases of IgA deficiency.
Adults with a positive blood test and those with negative antibodies where coeliac disease is suspected should be referred to a gastroenterologist.
Diagnosis in children
When requesting tests for children, laboratories should:
- test for total IgA and IgA tTG, as first choice test
- consider using IgG EMA, IgG DGP or IgG tTG in cases of IgA deficiency.
For children, a biopsy may not be necessary in every case. NICE recommends that children with a positive serological test are referred to a paediatric gastroenterologist or paediatrician with a special interest in gastroenterology for further investigation. Symptomatic children whose blood tests show a high level of IgA tissue transglutaminase antibodies (>10 x upper limit of normal for assay) and who are HLA-DQ2/ DQ8 positive may not need to undergo biopsy to secure diagnosis.
Children with a positive blood test and those with negative antibodies where coeliac disease is suspected should be referred to a paediatric gastroenterologist or paediatrician with a specialist interest in gastroenterology.
Total IgA should be measured when testing for coeliac disease. This is because IgA deficiency is more common in people with coeliac disease than the general population. People with IgA deficiency will have a false negative serological result when tested for IgA antibody, which may lead to a missed diagnosis of coeliac disease.
In individuals with IgA deficiency, IgG antibodies are recommended in place of IgA antibodies.
Advice before testing
It is important to inform people undergoing testing for coeliac disease that in order to get accurate test results, they should continue to eat a gluten containing diet before and during the diagnosis process. NICE recommends including gluten in more than one meal a day for at least six weeks before testing.
A gluten free diet should not be initiated until diagnosis is confirmed by a specialist, even if the results of a serological test are positive.
If people who have restricted their gluten intake or excluded gluten from their diet are unable to reintroduce gluten into their diet before testing, refer the patient to a gastroenterologist and explain that it may be difficult to confirm their diagnosis by intestinal biopsy.