Blood Tests: Even though an intestinal biopsy is considered the only way to definitively diagnose Celiac Disease, blood tests are usually performed first to see if a biopsy is necessary. If you have Celiac Disease, your body produces antibodies in reaction to ingesting gluten. The blood tests look for these antibodies. There are three specific blood tests that are performed, although all the blood needed can be taken in one draw. The three tests are:
IgA endomysial antibodies (EMA) – If you test positive for EMA, it is almost certain that you have Celiac Disease. EMA is almost 100% specific to Celiac Disease, but it is not 100% sensitive. Sometimes there are false negatives. Also, a small percentage of people with Celiac Disease do not make IgA antibodies. For them, this test would be negative even though they have Celiac Disease. That is why more than one test should be performed.
IgA tissue transglutaminase (tTG) – The test for tTG is not 100% specific. Positive results may indicate other issues such as diabetes, heart failure, and/or liver disease. It is also not 100% sensitive since some who have Celiac Disease can have a negative result. Once again, this is why more than one test is performed.
Total Serum IgA – Since some people are IgA deficient, this test looks for IgA deficiency. IgA deficiency will affect the accuracy of the other tests, so it is important to know.
*Note: The IgA and IgG antigliadin antibodies (AGA) test used to be performed as a test for Celiac Disease. It is no longer used since it is not as specific or sensitive as other blood tests.
Biopsies: Blood tests are not considered an actual diagnosis of Celiac Disease. Since none are 100% sensitive and/or specific, positive blood test results just show the need for a endoscopy/biopsy to get a conclusive diagnosis.
For the endoscopy/biopsy, patients are placed under conscious sedation so they don’t remember anything. A scope is put down through the throat and stomach to the small intestine, where several sections are biopsied. Since the flattening of the villi is usually not uniform, several biopsies are needed.
If Dermatitis Herpetiformis is suspected, a biopsy of the skin next to a blister is performed. If this test is positive, then an intestinal biopsy is not needed. A positive skin biopsy is a positive diagnosis for Celiac Disease.
*Note: Gluten Challenge - There is one problem for people who have already started on a gluten free diet. For the test results to be accurate, especially the biopsies, you need to have been eating gluten for one to three months before testing. Unfortunately, the amount of time needed to be eating gluten prior to testing is different for each person. That is why one to three months is recommended.