Policy for Tests for Coeliac Disease

Serum from patients with suspected coeliac disease will be assayed for IgA anti-tissue transglutaminase (tTg).

Samples positive for anti-tTg will be further tested for IgA anti-endomysial antibodies.

Anti-tTG Ab are determined using the Bioplex 2200.  This method includes an IgA verification test. If this fails, the sample will have immunoglobulin levels measured by nephelometry in order to detect IgA deficiency.

Samples shown to be IgA deficient will be assayed for IgG anti-endomysial antibodies.

Requests for anti-gliadin antibodies will receive IgA anti-tTg.

Immunoglobulin requests and screening tests for coeliac disease

Screening for coeliac disease in appropriate populations by serological testing for the presence of IgA antibodies to Tissue Transglutaminase (tTG) provides a highly sensitive and specific test for this condition. Individuals with IgA deficiency are present in cohorts of patients with coeliac disease at a greater frequency than in the general population. This has led to the frequent practice of requesting serum immunoglobulin quantification in addition to coeliac serology in order to identify patients with IgA deficiency. Whilst understandable, given the massive increase in requesting for coeliac serology, this practice has created a significant workload for the laboratory.

 

In July 2010 a laboratory audit identified that only 3% of samples tested for coeliac serology and serum immunoglobulin concentration at the same request had a serum IgA level of below 0.3g/L, a level that we consider has an increased risk of invalidating the IgA anti-tTG assay and which triggers the testing for the presence of IgG anti-endomysial antibodies. The majority of these would have been identified by our internal laboratory procedures and in none of these patients was the IgG anti-endomysial antibody test found to be positive. Where immunoglobulins were abnormal, the vast majority were found to have either elevated IgA or elevated IgG levels.

 

The policy for Coeliac screening is as follows:

 

Serum from patients with suspected coeliac disease will be assayed for IgA anti-tissue transglutaminase (tTg).  Anti-tTG Ab are detected on the Bioplex 2200 multiplex platform.  An IgA verification bead is included in this assay and is therefore able to detect patients who are IgA deficient which makes the requesting of IgA unnecessary. 

For all individuals over 6 years:

  •  Where only immunoglobulins are requested in addition to coeliac serology, IgA tTG ONLY will be performed as the first line test.
  •  If this result raises the possibility of IgA deficiency, measurement of IgA will be undertaken, (in addition to measurement of IgG endomysial antibodies as at present).

For all individuals under 6 years:

  • In addition to coeliac serology, immunoglobulin measurement will be performed.
  • If the result identifies IgA deficiency measurement of IgG endomysial antibodies will be performed.

Samples positive for anti-tTg will be further tested for IgA anti-endomysial antibodies.

Samples flagged on the Bioplex analyser to be potentially IgA deficient (fail the IgA verification bead test) will have immunoglobulin levels measured by nephelometry in order to detect IgA deficiency.

Samples shown to be IgA deficient will be assayed for IgG anti-endomysial antibodies.

Requests for anti-gliadin antibodies will receive IgA anti-tTg.

 

We are confident that these changes will continue to provide appropriate testing for the diagnosis and monitoring of coeliac disease.


Page updated: 10/10/14 | Updated by: Anna McHugh