Celiac disease testing typically starts with a simple blood test and, if results are positive, is confirmed with a biopsy of the small intestine. The process is straightforward, but the order matters, and one critical rule applies to every step: you need to be eating gluten for the tests to work.
The Blood Test That Starts the Process
The first test your doctor will order is a blood draw looking for specific antibodies your immune system produces when it reacts to gluten. The primary screening test measures an antibody called tTG-IgA (tissue transglutaminase IgA). It catches about 93% of people who have celiac disease and correctly rules it out about 96.5% of the time, making it one of the more reliable screening tools in medicine.
Your doctor may also check for a second antibody called EMA (endomysial antibody), which is highly specific for celiac disease. When both tests come back positive, the likelihood that you have celiac disease is very high. A third option, called DGP (deamidated gliadin peptide), is sometimes added to the panel, particularly for young children under age two where the primary test can be less reliable.
Along with these antibody tests, most doctors will check your total IgA level. About 2 to 3% of people with celiac disease have a condition called IgA deficiency, meaning their bodies don’t produce enough of this particular type of antibody. If you’re one of them, the standard tTG-IgA test could come back falsely negative. In that case, your doctor switches to IgG-based versions of the same tests, which work through a different antibody pathway and remain accurate even with low IgA.
Why You Must Be Eating Gluten
This is the single most important thing to know before getting tested: if you’ve already removed gluten from your diet, your antibody levels will drop and your test results may come back normal even if you have celiac disease. Your immune system only produces those telltale antibodies when it’s actively responding to gluten.
If you’ve already gone gluten-free and want an accurate diagnosis, you’ll need what’s called a gluten challenge. The traditional approach involves eating the equivalent of about four to six slices of bread per day (roughly 8 to 10 grams of gluten) for six to eight weeks before testing. A newer, modified version reduces that to about 3 grams a day, or roughly one and a half slices of bread, which is easier to tolerate and still produces enough of an immune response for accurate results. Neither option is pleasant if gluten makes you sick, but a confirmed diagnosis matters for long-term monitoring and care.
Confirming With an Intestinal Biopsy
A positive blood test points strongly toward celiac disease, but for most adults, the diagnosis is confirmed with a biopsy of the small intestine. This remains the gold standard. During an upper endoscopy, a gastroenterologist passes a thin, flexible tube through your mouth and into the upper part of your small intestine (the duodenum), where they take several tiny tissue samples. The procedure itself usually takes about 15 to 20 minutes, and you’re sedated for it.
A pathologist then examines those samples under a microscope, looking for the hallmark damage celiac disease causes: flattened or destroyed villi, the tiny finger-like projections that line your small intestine and absorb nutrients. The damage is graded on a scale, and the pattern of inflammation, combined with your blood work, gives a definitive answer. Multiple samples are taken because the damage can be patchy, appearing in some areas but not others.
Genetic Testing and What It Can Rule Out
Celiac disease requires specific genetic markers called HLA-DQ2 and HLA-DQ8. Virtually 100% of people with celiac disease carry one or both of these genes. But here’s the catch: roughly 30 to 40% of the general population carries them too, and most of those people will never develop celiac disease.
That makes genetic testing far more useful for ruling the disease out than for confirming it. If you test negative for both HLA-DQ2 and HLA-DQ8, you can be almost certain you don’t have celiac disease and won’t develop it in the future. Doctors find this particularly helpful in a few specific situations: when someone has already gone gluten-free and blood tests are inconclusive, when biopsy results are unclear, or when screening family members of someone with a confirmed diagnosis to determine who needs ongoing monitoring.
Rapid Finger-Prick Tests
Point-of-care tests that use a drop of blood from a finger prick do exist and can detect tTG-IgA antibodies in about five minutes. They’re appealing because they’re fast and accessible, but their accuracy doesn’t match laboratory blood tests. Studies have found they have high specificity (meaning a positive result is likely real) but lower sensitivity, catching roughly 78% of cases compared to over 90% for lab-based tests. That gap means they miss a meaningful number of people who actually have celiac disease. They can be a useful first step to encourage further testing, but a negative result on a rapid test doesn’t reliably rule anything out.
Testing for the Skin Form of Celiac Disease
Some people with celiac disease develop an intensely itchy, blistering rash called dermatitis herpetiformis, most commonly on the elbows, knees, buttocks, and back. If your doctor suspects this condition, the diagnostic approach is different: instead of (or in addition to) an intestinal biopsy, they’ll take a small skin biopsy.
The key detail is where the biopsy is taken. The sample needs to come from normal-looking skin right next to a lesion, not from the rash itself. Biopsies taken directly from the rash have a higher false-negative rate. Under a special type of microscopy called direct immunofluorescence, the pathologist looks for a specific pattern of granular IgA deposits at the junction between the outer and deeper layers of skin. This test has 90 to 95% sensitivity and 95 to 100% specificity. A positive skin biopsy is considered confirmation of celiac disease even without an intestinal biopsy, since the two conditions are directly linked.
How Celiac Testing Differs From Gluten Sensitivity
If your celiac blood tests and biopsy come back negative but you still feel terrible when you eat gluten, the next possibility your doctor will consider is non-celiac gluten sensitivity. The important distinction: there is currently no blood test, biopsy, or biomarker that can diagnose gluten sensitivity. Unlike celiac disease, it doesn’t trigger the same antibody response, and it doesn’t cause visible damage to the intestinal lining.
Diagnosis happens through elimination. Once celiac disease (and wheat allergy) have been ruled out, your doctor will typically recommend removing gluten from your diet for several weeks to see if symptoms improve, then reintroducing it to see if they return. If the pattern holds, gluten sensitivity is the working diagnosis. It’s a less precise process, which is why ruling out celiac disease first with proper testing is so important.