If your doctor suspects that you have celiac disease or gluten intolerance, he or she may use blood tests — also called serological tests — to look for antibodies that the body produces when someone with a sensitivity or celiac disease eats gluten.
You have to be eating gluten for an extended length of time before blood testing. If you don’t eat gluten, or haven’t eaten it for long enough, your body may not produce enough antibodies to show up on the tests, and the results will seem to show that you’re “normal” — or “negative” for gluten sensitivity or celiac disease.
No one knows for sure exactly how much gluten you need to be eating, but if you eat the equivalent of about one or two pieces of gluten-containing bread a day for at least three months, you should have enough gluten in your system to provide a measurable response. If you have severe symptoms during that time, consult your physician to see whether you should continue to eat gluten.
The most comprehensive panel of blood tests for gluten sensitivity and celiac disease includes five tests for antibodies:
tTG (anti-tissue transglutaminase)-IgA: This test is very specific to celiac disease, meaning that if you have a positive tTG, it’s very likely that you have celiac disease and not another condition.
EMA (anti-endomysial antibodies)-IgA: This test is also specific to celiac disease. When it’s positive, especially if tTG is positive too, it’s extremely likely that you have celiac disease.
AGA (antigliadin antibodies)-IgA: The antigliadin tests are less specific for celiac disease, and these antibodies sometimes show up in other diseases (including gluten sensitivity). AGA-IgA is useful when testing young children, who don’t always produce enough tTG or EMA for diagnostic purposes.
AGA-IgA is also useful for monitoring compliance on the gluten-free diet (if it’s still elevated after you’ve been gluten-free for several months, gluten may be sneaking into your diet). Some people feel that a positive AGA-IgA indicates gluten sensitivity.
AGA (antigliadin antibodies)-IgG: This is another antigliadin test (like the preceding one) and is less specific to celiac disease, but it may be useful in detecting gluten sensitivity or leaky gut syndrome.
Also, if the IgG levels are highly positive and all the other tests are negative, that may signal that the patient is IgA-deficient, in which case the results of the other tests are erroneous.
Total serum IgA (total serum, immunoglobulin A): A significant portion of the population is IgA-deficient, meaning their IgA production is always lower than normal. Three of the four tests above are IgA-based (the only one that isn’t IgA-based is antigliadin IgG), so in someone who’s IgA-deficient, results of those three tests would be falsely low.
By measuring total serum IgA, doctors can determine whether a patient is IgA-deficient and can compensate when reading the results of the three IgA-based tests.
Any lab can draw the blood, as long as you have an order from a health care practitioner allowed to order blood draws.
Celiac disease and gluten sensitivity can be triggered at any age, so just because you went to the doctor and tested negative once doesn’t mean you’re “out of the woods” forever.