Celiac disease is diagnosed through a combination of blood tests and, in most cases, a small intestine biopsy. The process typically starts with a simple blood draw that screens for specific antibodies your immune system produces in response to gluten. If those results are positive, an upper endoscopy with biopsy confirms the diagnosis by showing actual damage to the intestinal lining.
The First Step: Antibody Blood Tests
The primary screening test measures an antibody called tissue transglutaminase IgA (tTG-IgA). Your body produces this antibody when your immune system reacts to gluten, and the test catches celiac disease about 93% of the time with a specificity near 98%. That means false positives are rare, and a positive result is a strong signal that something real is going on. Your doctor will usually order this alongside a total IgA level, which matters because about 2% to 3% of people with celiac disease have an IgA deficiency. If your body doesn’t produce enough IgA overall, the standard test can come back falsely negative. In that case, IgG-based versions of the test are used instead.
A second antibody test, the endomysial antibody (EMA) test, is considered even more precise and has a specificity close to 100%. However, it’s more expensive, labor-intensive, and relies on subjective interpretation under a microscope, so it’s typically reserved as a confirmatory test rather than a first-line screen. Both tests require you to be actively eating gluten. If you’ve already cut gluten from your diet, the antibodies can drop to undetectable levels and the results become unreliable.
Confirming With an Intestinal Biopsy
A positive blood test alone isn’t enough for most adults. The American College of Gastroenterology recommends an upper endoscopy with biopsy to confirm the diagnosis. During the procedure, a thin flexible tube is passed through your mouth and into your small intestine. It takes about 10 to 15 minutes, and you’re sedated for it. The doctor collects several tiny tissue samples from the duodenum, the first section of your small intestine, where celiac damage is most visible.
A pathologist then examines those samples under a microscope, looking for a specific pattern of damage. In a healthy intestine, the lining is covered in tiny finger-like projections called villi that increase the surface area for absorbing nutrients. In celiac disease, the immune reaction to gluten gradually flattens these villi. The damage is graded on a scale: early stages show increased immune cells in the lining but intact villi, moderate stages show the villi shortening and the tissue reorganizing, and the most advanced stage shows complete loss of villi. A diagnosis is confirmed when the biopsy shows this characteristic pattern of villous damage alongside the positive blood work.
The biopsy also helps rule out other conditions that can mimic celiac disease, including certain infections, immune disorders, and medication reactions that can cause similar-looking intestinal changes.
When Children Can Skip the Biopsy
European guidelines, now widely referenced internationally, allow symptomatic children to be diagnosed without a biopsy under strict conditions. The child’s tTG-IgA level must be more than 10 times the upper limit of normal, and a separate blood sample must also test positive for EMA antibodies. If both criteria are met, the diagnosis is considered reliable enough to skip the endoscopy. This approach spares young children from sedation and an invasive procedure when the lab results are overwhelmingly clear. For adults, the no-biopsy pathway is still being studied and isn’t standard practice yet.
Genetic Testing: Ruling It Out
Genetic testing plays a unique role in celiac diagnosis. It doesn’t confirm the disease, but it can effectively rule it out. Celiac disease requires specific genetic markers called HLA-DQ2 or HLA-DQ8. If you don’t carry either gene, your chance of having celiac disease is essentially zero, with a negative predictive value approaching 100%. About 30% to 40% of the general population carries one of these genes, so having them doesn’t mean you have celiac disease. It just means it’s possible.
Genetic testing is most useful in a few specific situations: when someone has already gone gluten-free before being tested, when blood tests and biopsy results don’t agree, or when screening family members of someone with a confirmed diagnosis. A negative genetic result usually eliminates the need for any further celiac testing, including endoscopy.
The Gluten Challenge: When You’ve Already Gone Gluten-Free
If you stopped eating gluten before getting tested, your antibody levels and intestinal damage may have already started healing, which can cause both blood tests and biopsies to come back normal even if you do have celiac disease. In this situation, you’ll need a gluten challenge: deliberately reintroducing gluten before testing.
Current recommendations suggest eating 3 to 6 grams of gluten per day (roughly one to two slices of wheat bread) for at least 12 weeks to give the immune response enough time to become detectable. If gluten causes only mild or no symptoms, eating more, up to 10 grams per day, for longer increases the confidence that a negative result is truly negative. If symptoms are severe, an abbreviated challenge of 6 to 12 weeks may be acceptable, though a shorter challenge makes it harder to definitively rule celiac out. A check-in with your doctor around the 4 to 6 week mark helps adjust the plan based on how you’re tolerating it.
Diagnosing the Skin Form: Dermatitis Herpetiformis
Celiac disease doesn’t always show up as digestive symptoms. Some people develop dermatitis herpetiformis, an intensely itchy, blistering rash that typically appears on the elbows, knees, buttocks, and back. This rash is diagnosed through a skin biopsy, but not from the rash itself. The sample must be taken from normal-looking skin right next to an active lesion. A lab technique called direct immunofluorescence then looks for a specific pattern of IgA antibody deposits in the skin. This test has sensitivity and specificity close to 100%, making it extremely reliable. A positive result confirms both dermatitis herpetiformis and the underlying celiac disease.
If you’ve already been on a gluten-free diet, these IgA deposits can fade from the skin over weeks to months, potentially causing a false negative. In that case, you may need to eat gluten for at least a month before the skin biopsy.
Capsule Endoscopy for Special Cases
In some situations, a pill-sized camera that you swallow (capsule endoscopy) can be used instead of or alongside traditional endoscopy. This is most helpful for people who are unable or unwilling to undergo standard endoscopy, or for those with an established celiac diagnosis who develop worrying symptoms like unexplained weight loss, persistent abdominal pain, or iron deficiency that doesn’t respond to supplements. Studies report sensitivity ranging from about 85% to 95% for detecting the villous damage characteristic of celiac disease. The capsule also allows visualization of the entire small intestine, not just the upper portion, which is valuable when looking for complications in long-standing disease.