Usually, initial celiac disease testing involves the detection of specific autoantibodies, followed by a biopsy to confirm a diagnosis of celiac disease. Autoantibody testing is performed to diagnose and monitor celiac disease, primarily in symptomatic people, but also may be used to screen close family members of a person who has been diagnosed with the disease.
Tests that detect two different classes of the autoantibodies, IgA and IgG, are available, but the IgA tests are more specific and are used almost exclusively. IgA is the primary antibody present in gastrointestinal secretions. However, about 2-3% of people with celiac disease have an IgA deficiency, which can lead to false-negative test results. In these cases, IgG autoantibody tests may be ordered.
Common celiac disease antibody testing includes:
- Anti-tissue Transglutaminase (anti-tTG) antibodies, IgA: this is the most sensitive and specific blood test for celiac disease and is typically the initial test performed. The test for the IgG class of anti-tTG is less sensitive and specific than the IgA class but may be ordered when a person has an IgA deficiency.
- Quantitative Immunoglobulin A (IgA): this test is sometimes ordered in conjunction with an anti-tTG test to detect IgA deficiency.
- Deamidated Gliadin Peptide (DGP) antibodies, IgA: this test may be positive in some people with celiac disease who are negative for anti-tTG, especially young children; DGP IgG testing along with anti- tTG IgG is recommended by the American College of Gastroenterology for those who have low IgA or IgA deficiency.
Less common autoantibody tests include:
- Anti-Endomysial Antibodies (EMA), IgA: may provide additional information if the primary test results are not clear, but it is more difficult to perform than anti-tTG
- Anti-Reticulin Antibodies (ARA), IgA: not as specific or sensitive as other tests and rarely ordered
(For more detail on the above tests, see the article on Celiac Disease Antibody Tests.)
To confirm a diagnosis of celiac disease, a biopsy of the small intestine is examined to detect damage to the intestinal villi. (For general information on biopsies, read the article on Histopathology.)
Genetic tests that look for the markers that are strongly associated with celiac disease are available but not routinely ordered. These tests include the Human Leukocyte Antigen (HLA) markers DQ2 and DQ8. They are most useful for family members of individuals with the disease who fall into a high risk category and for those with other diagnostic test results that are inconclusive.
- A positive result does not diagnose celiac disease since about 30% of the general population also carry these markers but do not have the disease.
- A negative result, however, can essentially rule out celiac disease in those individuals for whom results of other tests, including biopsy, are unclear.
- Anti-Actin IgA (F-actin): the presence of this autoantibody in the blood is associated with more severe intestinal damage.
- Complete blood count (CBC) to look for anemia
- Erythrocyte sedimentation rate (ESR) to detect inflammation
- C-Reactive protein (CRP), a more sensitive measure of inflammation
- Comprehensive metabolic panel (CMP) to determine electrolyte, protein, and calcium levels and to evaluate the health of the kidneys and liver
- Vitamin D, vitamin B12 and folate to detect vitamin deficiencies
- Iron, iron binding capacity or transferrin, and ferritin to detect iron deficiency
- Stool fat, to help evaluate malabsorption
Sometimes tests may be done to rule out other conditions. These tests may include:
X-rays of the intestines after barium ingestion may show characteristic findings that indicate intestinal damage.