Coeliac disease update

Our new pathway reduces the risk of missing IgA-deficient patients.

Coeliac disease is an immune-mediated disease of the intestines that is triggered by the ingestion of gluten in genetically susceptible individuals. Gluten is the major protein component of wheat, rye, and barley. Genetic predisposition does play a key role in Coeliac disease, and it is well known that Coeliac disease is strongly associated with specific HLA class II genes known as HLA-DQ2 and HLA-DQ8. Approximately 95% of Coeliac disease patients express HLA-DQ2, and the remaining patients are usually HLA-DQ8 positive. The negative predictive value for both tests is higher than 99%. However, the HLA-DQ2 allele is common and is carried by approximately 30% of Caucasian individuals. Thus, HLA-DQ2 or HLA-DQ8 is necessary for disease development but is not sufficient for disease development; its estimated risk effect is only 36-53%.

Note: History taking is important if a patient has been on a gluten-free diet for 6-12 months, approximately 80% will lose their antibody response. After 5 years this increases to >90%.

New pathway

To determine the new Coeliac Pathway, a TDL audit of more than 12,000 requests for coeliac testing was carried out and results assessed within UKAS current guidelines. The purpose of these new guidelines is to reduce the risk of missing IgA deficient patients.

The new pathway covers this by adding a total IgA to all low Tissue Transglutaminase (TGG) IgA results to check for an IgA deficiency. If an IgA deficiency is identified, a reflex deamidated gliadin IgG will be carried out to determine whether the patient is likely to have coeliac disease with an IgG antibody.

The changes are as follows:

Initial TTG IgA samples are received and tested
If TTG IgA is LOW <0.2 U/ml reflex testing for Total IgA will be undertaken
If Total IgA is LOW <0.1 g/L then reflex testing for Gliadin IgG test will be undertaken
If TTG IgA is HIGH (>/= 10 U/ml), then reflex testing for Endomysial IgA will be undertaken as a confirmatory test.

Endomysial IgA

This is no longer available as a stand-alone test. If requested the request will default to TTG IgA.
However, if TTG IgA is positive, endomysial IgA will be carried out as a confirmatory test. This only needs to be done once in the patient's history.

Endomysial IgG requests

No longer available as a single test request.

Deamidated gliadin IgA requests

This is no longer available. If requested, the request will default to TTG IgA.

Deamidated gliadin IgG requests

This can be requested as an individual standalone test as well as being incorporated into the coeliac pathway. This may be useful when testing children’s samples.

Appropriate clinical comments will be added to results automatically – as follows:

TTG IgA result U/ml	Total IgA result for new assay g/L	Deamidated gliadin IgG result U/ml	Comment
0.2 to 10	N/A	N/A	Coeliac disease unlikely (please note that if the patient has no dietary gluten results may appear false negative)
>/= 10	N/A	N/A	Suggestive of coeliac disease
<0.2	>/= 0.1	N/A	Coeliac disease unlikely (please note that if the patient has no dietary gluten, results may appear false negative)
<0.2	<0.1	>/=10	Consistent with coeliac disease in a patient with selective IgA deficiency
<0.2	<0.1	< 7	Coeliac disease unlikely (please note that if the patient has no dietary gluten, results may appear false negative)
<0.2	<0.1	7-10	Result equivocal suggest referral to a gastroenterologist for consideration of duodenal biopsy