Celiac disease antibody tests are primarily used to help diagnose and monitor celiac disease, an autoimmune disorder caused by an inappropriate immune response to gluten, a protein found in wheat, and related dietary proteins in rye and barley. Celiac tests are usually ordered for people with symptoms suggesting celiac disease, including anemia and abdominal pain.

Sometimes celiac testing may be used to screen for asymptomatic celiac disease in those who have close relatives with the disease since about 4-12% of them have or will develop celiac disease. Testing may also be ordered in those who have other autoimmune diseases.

Celiac disease blood tests measure the amount of particular antibodies in the blood. The most common tests include:

• Tissue transglutaminase antibody (tTG), IgA class — the primary test ordered to screen for celiac disease. It is the most sensitive and specific blood test for celiac disease and is the single test preferred by the American College of Gastroenterology, according to its 2013 guidelines, as well as the American Gastroenterology Association for the detection of celiac disease in those over the age of 2 years. The IgG class of anti-tTG may be ordered as an alternative in those who have a deficiency of IgA.If the anti-tTG, IgA or IgG test is positive, then the test can also be used to monitor a person with celiac disease and to help evaluate the effectiveness of treatment; antibody levels should fall when gluten is removed from the diet. Although "tissue" is in the name of these tests, they are measured in the blood.
• Quantitative immunoglobulin A (IgA) test — ordered along with, prior to, or following an anti-tTG test to detect IgA deficiency, which occurs about 2-3% of the time in people with celiac disease and can lead to false-negative test results. If a person has an IgA deficiency, then a test to detect the IgG class of autoantibodies may be ordered.
• Deamidated gliadin peptide (DGP) antibodies (anti-DGP), IgA or IgG — may be positive in some people with celiac disease who are negative for anti-tTG, especially children less than 2 years old. It may sometimes be ordered with or following an anti-tTG test, especially if anti-tTG is negative. DGP IgG testing along with anti-tTG IgG is recommended by the American College of Gastroenterology for people who have low IgA or IgA deficiency.If the anti-DGP test is positive, it may be used to monitor celiac disease.

Test that are used less often include:

• Anti-endomysial antibodies (EMA) -— antibodies developed in reaction to the ongoing damage to the intestinal lining; it has been found that tTg is the substance detected in this test. Almost 100% of people with active celiac disease and 70% of those with dermatitis herpetiformis (another gluten-sensitive condition that causes an itchy, burning, blistering rash on the skin) will have the IgA class of anti-EMA antibodies. The test is more difficult to do and interpret properly than anti-tTg so it is used less often.
• Anti-reticulin antibody (ARA) test — not as specific or sensitive as the other autoantibodies; it is found in about 60% of people with celiac disease and about 25% of those with dermatitis herpetiformis; it is rarely ordered.

To confirm a diagnosis of celiac disease, a biopsy of the small intestine is examined to detect damage to the intestinal villi. However, given the invasive nature and cost of a biopsy, antibody tests are often used to identify those individuals with high probability of having celiac disease. (For general information on biopsies, see the article on Histopathology.)

Other tests may be ordered to help determine the severity of the disease and the extent of the complications a person may experience, such as malnutrition, malabsorption, and the involvement of other organs. Tests may include:

• Anti-F-actin — may sometimes be ordered if a person has been diagnosed with celiac disease and a health practitioner wants to evaluate the severity of intestinal damage; a positive result may indicate increased intestinal damage.
• CBC (complete blood count) to look for anemia
• ESR (erythrocyte sedimentation rate) to evaluate inflammation
• CRP (C-Reactive protein) to evaluate inflammation
• CMP (comprehensive metabolic panel) to determine electrolyte, protein, and calcium levels, and to verify the status of the kidney and liver
• Vitamin D and B12 and folate to measure vitamin deficiencies
• Iron, iron binding capacity or transferrin, and ferritin to detect iron deficiency
• Stool fat, to help evaluate malabsorption

Since those with celiac disease may also experience conditions such as lactose intolerance, celiac tests may be done in conjunction with other intolerance and allergy testing. 

Celiac disease tests are ordered when someone has signs and symptoms suggesting celiac disease, malnutrition, and/or malabsorption. The symptoms are often nonspecific and variable, making the disease difficult to spot. The symptoms may, for a time, be mild and go unnoticed and then progressively worsen or occur sporadically. The condition can affect different parts of the body.

Gastrointestinal signs and symptoms may include:

• Abdominal pain and distension
• Blood stool
• Chronic diarrhea or constipation
• Flatulence
• Greasy, foul-smelling stools
• Vomiting

Other signs and symptoms may include:

• Iron-deficiency anemia that does not respond to iron supplements
• Easy bruising and/or bleeding
• Bone and joint pain
• Defects in dental enamel
• Fatigue, weakness
• Mouth ulcers
• Weight loss
• In adults, infertility, osteoporosis

In children, celiac disease tests may be ordered when a child exhibits:

• Gastrointestinal symptoms
• Delayed development
• Short stature
• Failure to thrive

Many people with celiac disease have dermatitis herpetiformis, a disease that causes itchy blisters on the skin. There is also an increased risk for developing osteoporosis and intestinal lymphoma, a form of cancer.

One or more antibody tests may be ordered when someone with celiac disease has been on a gluten-free diet for a period of time. This is done to verify that antibody levels have decreased and to verify that the diet has been effective in reversing the intestinal lining damage (this is sometimes still confirmed with a second biopsy).

Asymptomatic people may be tested if they have a close relative such as a parent or sibling with celiac disease, but celiac disease testing is not recommended at this time as a screen for the general population.

All positive and indeterminate celiac disease tests are typically followed by an intestinal biopsy.A biopsy is used to make a definitive diagnosis of celiac disease.

If someone has been diagnosed with celiac disease and eliminates gluten from his or her diet, then the autoantibody levels should fall. If they do not fall and the symptoms do not diminish, then there may either be hidden forms of gluten in the diet that have not been eliminated (gluten is often found in unexpected places, from salad dressings to cough syrup to the adhesive used on envelopes) or the person may have one of the rare forms of celiac disease that does not respond to dietary changes. When celiac disease tests are used to monitor progress, rising levels of autoantibodies indicate some form of noncompliance with a gluten-free diet.

If the person being tested has not consumed any gluten for several weeks to months prior to testing, then celiac disease tests may be negative. If the health practitioner still suspects celiac disease, he or she may do a gluten challenge – have the person introduce gluten into his or her diet for several weeks or months to see if the symptoms return.At that time, celiac disease tests may be repeated or a biopsy may be done to check for damage to the villi in the intestine.

Historically, a test for anti-gliadin antibody (AGA) was used in the evaluation of celiac disease. The 2013 American College of Gastroenterology guidelines recommend against this test for the primary detection of celiac disease due to concerns with its accuracy. It is inferior to the tests for anti-tTG and anti-DPG and should no longer be part of routine testing for celiac disease. The American Gastroenterology Association makes similar recommendations.

Although celiac disease is relatively common (about 1 in 100 to 150 people in the U.S. are thought to be affected), most people who have the disease are not aware of it. This is partly due to the fact that the symptoms are variable -- they may be mild or absent, even when intestinal damage is present on biopsied tissue. Since these symptoms may also be due to a variety of other conditions, a diagnosis of celiac disease may be missed or delayed, sometimes for years.