Important information
We are adjusting the way we perform coeliac serology screens in line with others services in the region. From 27/07/22 you will no longer automatically receive a total serum Immunoglobulin A concentration with every coeliac serology request.
Currently our first line screen consists of two assays: a total IgA serum concentration measurement [IgA] and an IgA-tissue Transglutaminase (IgA-tTG) antibody test. We (and many others) have found that the IgA-tTG antibody assay data (RU value) can be used to predict which serum samples actually require a total serum IgA measurement (this data is available on request from Immunology).
Any serum sample that is flagged as having a low RU value will automatically receive a total IgA measurement. If the total serum IgA concentration is <0.2 g/L the usual IgG serology assays (IgG-tTG/IgG-EMA) will be reflexed, as already occurs for any patients with a serum total IgA concentration of <0.2g/L.
This will allow us to reduce unnecessary total IgA measurements by >95% resulting in significant efficiency savings.
For any additional information please contact the Immunology laboratory.
Description
Untreated coeliac disease is characterised by the presence of IgA antibodies to one or more antigens. IgA anti-tissue transglutaminase antibodies are now used as the screening test of choice. All positive samples are then tested for IgA anti-endomysial antibodies. There is a good correlation with disease activity. The widespread use of these tests has led to the realisation that coeliac disease is common in all age groups even the elderly and presentation can be varied. An immune response to tissue transglutaminase or its products is the cause of coeliac disease.
Most untreated coeliacs will have both IgA anti-tTg and endomysial antibodies. IgA anti-tTg tends to appear before anti-endomysial, sometimes before overt symptoms. On a gluten free diet IgA anti-tTg usually disappears after IgA anti-endomysial. Relapse or poor compliance with a gluten free diet is often associated with return of antibody positivity.
Note that coeliac disease is often associated with IgA deficiency. IgA levels are estimated in all patients with suspected coeliac disease. IgA deficient individuals with suspected coeliac disease are tested for IgG anti-tTg and IgG anti-endomysial antibodies. The test for IgA anti-TTg will usually detect IgA deficiency and indicate the need for measurement of IgG antibodies.
Occasionally the standard autoantibody screen will identify anti-reticulin autoantibodies which can suggest coeliac disease. In such cases, the serum will be tested for IgA anti-TTg.
Indication
Coeliac disease. Failure to thrive in children, gut disorders, malnutrition, anaemia or osteoporosis in adults. Note that coeliac disease is now diagnosed for the first time in patients of any age.
Interpretation
Samples positive for both IgA anti-TTg and endomysial antibodies are almost certainly from patients with coeliac disease or dermatitis herpetiformis. Samples positive only for IgA anti-TTg may suggest evolving coeliac disease. The commonest cause of ‘false positive’ IgA anti-tTg is a raised total IgA associated with chronic liver disease. Such patients seldom have anti-endomysial antibodies.
Sample
Serum Separator Tube (SST)
Assay details
Various; See anti-tTg and anti-endomysial.
Restrictions
None
Reference range
See individual tests
Assay range notes
See individual tests
Turnaround time
3 – 5 days
Analysing laboratory
Immunology The James Cook University Hospital