Making the diagnosis of celiac disease has always been difficult, so difficult that many people go undiagnosed. The availability of better tests for gluten intolerance has made it much easier for doctors to diagnose the disease. These tests have been developed because of a greater understanding of the way gluten damages the small intestine. As a consequence of better tests, doctors have learned that there is a great deal of variety in the symptoms of patients with celiac disease.
The best test for any disease is called the “gold standard.” The “gold standard” test for celiac disease is a biopsy of the small intestine that shows damage to the cells lining the intestine. There are a variety of changes that can be seen under the microscope, depending on the degree of damage. The worst biopsies show an absence of intestinal villi, the projections of the lining cells that help nutrients get in. Patients should be on a diet containing gluten when scheduled for the biopsies.
To be done correctly, between four and six tiny pieces of the small intestine should be removed. The doctor who looks at the biopsies must know what to look for and be familiar with the appearance of this tissue in patients with gluten intolerance. If a patient’s biopsy is consistent with celiac disease, a gluten-free diet should be started. In the past, a second biopsy would be done to see if improvement in symptoms went along with an improvement in the appearance of the small intestine. At this time, most doctors do not do a second set of biopsies but follow the patient in other ways.
One set of small intestinal biopsies establishing the diagnosis of celiac disease is necessary. A person should not stay on a gluten-free diet forever unless there is no doubt about the diagnosis.
In the past, blood tests for celiac disease were not very good at either making the diagnosis or excluding the diagnosis of celiac disease. These tests had many both false positives and false negatives. A false positive test is when a person without the disease has a test result that is positive. This person would get the wrong diagnosis. A false negative test is when a person with a disease has a negative test. This person’s illness would be missed.
The oldest test which measures antibodies to gliadins (AGA IgA), one of the pieces of gluten, was not reliable. It only picked up 85 to 90% of patients with actual disease. That means that as many as 15% of patients with celiac disease would have a negative test. Also, 10% of the time, a person without celiac disease could have a positive test.
Patients with celiac disease have elevations of a substance called human tissue transglutaminase (htTG) and they make antibodies to it. There is a test to measure these antibodies, called anti-tissue transglutaminase IgA htTG. This is the best test at the current time to find individuals with celiac disease. When the test is done correctly, 98.3% of patients with a positive test do have celiac disease. Out of 100 patients with celiac disease, only 4.9 might not have a positive test.
Patients do not always need to be eating gluten to take this test, because the test stays positive for three to 12 months after initiation of a gluten-free diet. So if a person has recently eliminated gluten from his or her diet, the test may still be positive. It can also be used to follow patients after diagnosis. This test requires only a fingerstick amount of blood. It may be possible to do this test on saliva in the future.
A second blood test is still used, called IgA EMA. The EMA stands for endomycial antibodies. This test is also very good at finding patients with celiac disease. It is a more difficult test to do right than anti-htTG IgA and it takes longer to get a result. In the right hands it is a very good test. Using the best substances for this test, 99.6% of the patients with a positive test will have celiac disease. Only 2.6 of those with a negative test have celiac disease. This test, called EMA, is a good test to follow patients after diagnosis.
In the past, a second small bowel biopsy was performed to look for improvement after a period of time on a gluten-free diet. Currently, most doctors will follow a patient’s symptoms as well as one or two blood tests to determine whether or not the disease is getting better.
Doctors need to have an awareness of the symptoms of celiac disease. In a patient with “classic” disease, anti-htG or EMA should be done. Doctors should know the reliability of the labs they use. A positive test needs to be followed by a small bowel biopsy while the patient is eating gluten.
If the doctors and laboratory doing the tests and looking at the biopsies are good at their jobs, the combination of a positive small bowel biopsy and positive IgA htTG are enough to diagnose celiac disease. Follow up can usually be done with blood tests.
A negative blood test in a patient whose history and other abnormalities point toward celiac disease probably needs a biopsy as well.
A patient with less clear symptoms who may not have celiac disease can have the blood tests performed, and if they are negative, it is usually not necessary to do a biopsy. A positive blood test must still be followed by a biopsy.
If you believe you have not been diagnosed properly, you should try and see a specialist (a gastroenterologist) who is knowledgeable at deciphering all this information. You can ask for the specific blood tests by name – anti-tissue transglutaminase (IgA htTG) and/or or endomycial antibodies (IgA EMA).