Celiac disease is diagnosed through a combination of blood tests and, in most cases, a biopsy of the small intestine. The process typically starts with a simple blood draw that checks for specific antibodies your immune system produces in response to gluten. Getting tested in the right order, and while you’re still eating gluten, is critical for accurate results.
The First Step: Blood Tests
The preferred screening test is called the tTG-IgA test, which looks for antibodies that target an enzyme in your small intestine. It has a sensitivity of 78% to 100% and a specificity of 90% to 100%, meaning it catches most cases and rarely flags people who don’t have the disease. Your doctor orders this as a standard blood draw, and results typically come back within a few days.
If the tTG-IgA result is positive or borderline, a second antibody test called the EMA-IgA test is sometimes used to increase confidence in the diagnosis. This test is even more specific, correctly ruling out celiac disease 97% to 100% of the time. A third option, the DGP test, exists but is less accurate than either of the other two and is mainly used in special circumstances.
One important caveat: about 2% to 3% of the general population has a condition called selective IgA deficiency, which makes all IgA-based blood tests unreliable. If you fall into this group, your doctor should order IgG versions of the same tests instead. Many labs now check your total IgA level alongside the celiac panel to catch this issue automatically.
Why You Must Be Eating Gluten
Both blood tests and biopsies depend on your body actively reacting to gluten. If you’ve already gone gluten-free before getting tested, your antibody levels may have dropped and your intestinal lining may have started healing, producing a false negative. This is one of the most common reasons people get inconclusive results.
If you’ve already removed gluten from your diet, you’ll need to do what’s called a gluten challenge: eating roughly one to two slices of bread per day (or an equivalent serving of pasta, cereal, or crackers) for four to eight weeks before testing. As little as 3 grams of gluten daily may be sufficient, though most guidelines recommend a full serving. Yes, this means intentionally eating the food that makes you feel terrible, but without it, doctors can’t reliably confirm or rule out the disease.
Confirming the Diagnosis With a Biopsy
A positive blood test alone doesn’t confirm celiac disease in most adults. The next step is an upper endoscopy, where a gastroenterologist passes a thin, flexible tube through your mouth and into your small intestine to collect tissue samples. The procedure takes about 15 to 20 minutes, is done under sedation, and you go home the same day. You won’t feel pain during the procedure, though mild throat soreness afterward is common.
Guidelines from the American College of Gastroenterology recommend taking at least four tissue samples from the lower part of the duodenum (the first section of your small intestine) plus one or two from the duodenal bulb. Multiple samples are necessary because celiac damage can be patchy, affecting some areas while sparing others. A targeted approach that includes the bulb reaches a diagnostic sensitivity of 96%.
A pathologist then examines the samples under a microscope and assigns a score based on the degree of damage. The scoring system runs from Type 0 (normal tissue) through Type 3c (complete destruction of the finger-like projections, called villi, that line the intestine and absorb nutrients). Types 3a through 3c, which show varying degrees of villous atrophy along with other inflammatory changes, are considered diagnostic for celiac disease. Types 1 and 2 show inflammation without villous damage and can occur in celiac disease but also in other conditions, so they require clinical context to interpret.
When Children Can Skip the Biopsy
European guidelines now allow a no-biopsy diagnosis in children when certain strict criteria are met. If a child’s tTG-IgA level is at least 10 times the upper limit of normal on an accurate, calibrated test, and a second blood sample confirms positive EMA-IgA antibodies, the diagnosis is considered secure without endoscopy. This approach has been validated as safe and spares children the sedation and discomfort of a procedure.
The threshold matters: the tTG-IgA must be 10 times the upper limit, not just mildly elevated. And the confirmatory EMA test must be run on a separate blood draw, not the same sample. Children who fall below this threshold still need a biopsy. Some adult gastroenterologists have begun adopting a similar approach for adult patients with very high antibody levels, though this remains less standardized.
Genetic Testing and Its Limits
Two genes, HLA-DQ2 and HLA-DQ8, are present in virtually all people with celiac disease. But carrying one or both of these genes doesn’t mean you have or will develop the condition. Roughly 30% to 40% of the general population carries these genes, and only a small fraction ever develops celiac disease.
Genetic testing is most useful as a rule-out tool. If you test negative for both HLA-DQ2 and HLA-DQ8, celiac disease is extremely unlikely, and you can essentially take it off the table. This makes genetic testing valuable in a few specific situations: screening family members of someone with celiac disease, evaluating people who went gluten-free before getting a proper workup, or clarifying an ambiguous biopsy result.
Testing for Dermatitis Herpetiformis
Some people with celiac disease develop an intensely itchy, blistering skin rash called dermatitis herpetiformis, often on the elbows, knees, buttocks, or scalp. If your doctor suspects this rash, the diagnostic approach is different from the standard celiac workup.
A skin biopsy is taken from uninvolved skin about 3 millimeters away from an active lesion, not from the rash itself. The sample is examined using a technique called direct immunofluorescence, which reveals a characteristic pattern of antibody deposits in the skin. Celiac blood tests should be run at the same time, since dermatitis herpetiformis is considered a skin manifestation of celiac disease and nearly all affected individuals have some degree of intestinal damage.
When Blood Tests Come Back Negative
About 15% or fewer of people with confirmed celiac disease are “seronegative,” meaning their blood tests don’t show the expected antibodies despite having intestinal damage. This can happen for several reasons: IgA deficiency (discussed above), being on a gluten-free or low-gluten diet before testing, immunosuppressive medications, or testing very early or very late in the disease process.
If your blood tests are negative but your symptoms strongly suggest celiac disease, your doctor may still recommend a biopsy. Genetic testing can also help in this scenario. If you lack both HLA-DQ2 and HLA-DQ8, celiac disease is essentially ruled out, and your doctor will look at other causes like irritable bowel syndrome, small intestinal bacterial overgrowth, or non-celiac gluten sensitivity.
At-Home Tests
Several at-home celiac screening kits are available online and in pharmacies. Some use a finger-prick blood sample to check for tTG-IgA antibodies, similar to a clinical lab test but with less precision. Others detect gluten fragments in your urine after exposure. Research from Columbia University has confirmed that the urine-based tests do successfully identify gluten if you’ve been exposed, but no study has yet demonstrated that using these tests actually improves outcomes for people with celiac disease.
At-home kits are not a substitute for clinical testing. A positive result still requires confirmation through standard blood work and likely a biopsy. A negative result could be falsely reassuring, particularly if you haven’t been eating enough gluten or if you have IgA deficiency. If you suspect celiac disease, starting with your doctor ensures the right tests are done in the right order and while you’re still eating gluten.