There are now good blood tests for celiac disease. They can be used as screening tests for people at risk for celiac disease. They can also be used to get a probable diagnosis of celiac disease in someone with symptoms. They may have to be relied on if a person is off of gluten, at which time intestinal biopsies might be normal. The blood test can stay positive for 3 to 12 months after a person with celiac disease stops eating gluten.
Older antibody tests were not as good as today’s tests, the tTGA or anti-tissue transglutaminase antibody test as well as the endomysial antibody test or EMA. These tests require blood samples and are done in a laboratory. There is more than one way to perform each test and more than one company making the kits used to do the tests. There is a large variability between labs, between test types and between test kits. Labs that tend to run a lot of tests tend to be quite reliable, while labs that are not as specialized may have poorer results. In general, the newer techniques are better than the old ones, and the labs with the most practice get the best results.
There have been clinical studies looking at this phenomenon and proving that there are differences between laboratories. In one study, the researchers were looking at the tTGA test. They discovered that it was not as accurate as some other researchers and studies have found. They also found a large difference in the results between labs. The sensitivity of the test was 40% at one lab and 86.4% at another. Both were “commonly used” laboratories. At the one lab, of 100 people with celiac disease, only 40 of them would have a positive test, which is not good. At the other lab, 80 of the 100 people with celiac disease would have a positive test. This is better but still not good.
The specificities were also different. At the first lab the specificity was 100% but the second lab’s specificity was 41.7%. That means that of out of a hundred patients without CD, none would test positive at the first lab, which is good. At the second lab, about 58 out of 100 people without CD would get a false positive test which is clearly not good.
These kinds of results cannot help anyone make a diagnosis. It is thought, however, at this time that most reliable labs get good results. If you are concerned about this in general, or because you had a surprising test result, you should talk to your healthcare provider about it. If you are seeing a gastroenterologist (a specialist in intestinal diseases) they would perform a small bowel biopsy if necessary to confirm you have celiac disease. That type of doctor should know how good the lab he or she uses is. As a matter of fact, they might recommend a particular lab for these tests as opposed to a regular lab they use all of the time for routine tests of other kinds.
If you are not seeing a specialist, you should ask your doctor to find out how good the results are at the lab he or she uses. If your doctor cannot help you or will not help you get the answer, you need to see a specialist.
As time goes on, laboratories get better at doing tests like these. The test procedures themselves get better. Sometimes newer, better tests are developed and the tests you are getting now may not be the ones used in the future.
Researchers in this field are aware that results of these tests vary from one lab to another. They are hoping to get standards set in the United States for these tests and their interpretation. Usually doctors who order a test frequently learn which laboratories in their area are the most reliable. They will pick the best lab, and also use their clinical experience in order to interpret results and decide if other tests need to be done.
All laboratories are not equal for these particular tests, and people who are being evaluated for celiac disease should be able to ask their doctors about the lab being used.