From the Guidelines
The most appropriate blood test to confirm coeliac disease is the IgA anti-tissue transglutaminase (tTG) test, along with total immunoglobulin A (IgA) measurement, as recommended by current guidelines and supported by the most recent systematic review with meta-analysis 1. When diagnosing coeliac disease, it is essential to consider the patient's symptoms, medical history, and risk factors. The IgA tTG test has high sensitivity and specificity for coeliac disease, detecting antibodies that the body produces in response to gluten exposure. Some key points to consider when ordering blood tests for coeliac disease include:
- Total serum IgA should be measured simultaneously with the IgA tTG test because about 2-3% of coeliac patients have IgA deficiency, which could lead to false-negative results.
- If IgA deficiency is present, alternative tests such as IgG endomysial antibodies (EMA), IgG deamidated gliadin peptide (DGP), or IgG tTG can be used.
- Patients should maintain their regular gluten intake before testing, as eliminating gluten prematurely can lead to false-negative results and complicate diagnosis.
- Current guidelines recommend that adults and children with suspected coeliac disease first undergo serological testing for total IgA and IgA anti-tissue transglutaminase (tTG) 1.
- In adults, weakly positive for IgA tTG, IgA EMA should be measured, and seropositive adults should be referred for intestinal biopsy, while seropositive children should be referred for further investigation, which may include intestinal biopsy, IgA EMA, human leukocyte antigen (HLA) genetic testing, or a combination of the above 1.
From the Research
Blood Tests for Coeliac Disease
The following blood tests can be used to confirm coeliac disease:
- IgA tissue-transglutaminase antibodies assay, which has a high sensitivity and specificity for diagnosing coeliac disease 2, 3
- IgG tissue-transglutaminase antibodies assay, which is useful for diagnosing coeliac disease in patients with selective IgA deficiency 4, 5
- IgA anti-endomysium antibodies test, which has a high specificity for coeliac disease but may be less sensitive than the tissue-transglutaminase antibodies assay 2, 3
Diagnostic Effectiveness
The diagnostic effectiveness of these blood tests is as follows:
- IgA tissue-transglutaminase antibodies assay: sensitivity of 95.8-100% and specificity of 95.3-97% 2, 3
- IgG tissue-transglutaminase antibodies assay: sensitivity of 98.7% and specificity of 98.6% in patients with selective IgA deficiency 4
- IgA anti-endomysium antibodies test: sensitivity of 83-100% and specificity of 95-100% 2, 3, 6
Monitoring Dietary Compliance
The tissue-transglutaminase antibodies assay can also be used to monitor dietary compliance in patients with coeliac disease, as it can detect small amounts of gluten intake 2