Testing for gluten intolerance depends on whether you’re dealing with celiac disease or a less defined condition called non-celiac gluten sensitivity. Celiac disease has a clear diagnostic path involving blood tests and sometimes a tissue sample from your small intestine. Non-celiac gluten sensitivity, on the other hand, is diagnosed only after celiac disease and wheat allergy have been ruled out. Here’s what each step of testing looks like and what to expect.
The First Step: A Blood Test
The standard screening for celiac disease is a blood test that looks for specific antibodies your immune system produces when it reacts to gluten. The most commonly ordered test measures an antibody called tTG-IgA. A second antibody test, called EMA-IgA, is sometimes run alongside it for confirmation. Together, these tests are highly reliable for initial screening, with sensitivity around 90% to 95% in people who are actively eating gluten.
Your doctor will order these through a standard blood draw. Results typically come back within a few days. If your tTG-IgA levels come back elevated, the next step is usually an intestinal biopsy to confirm the diagnosis. One important exception exists for children: European guidelines now allow a diagnosis without biopsy when tTG-IgA levels are at least 10 times the upper limit of normal and a second blood sample confirms positive EMA-IgA antibodies.
You Need to Be Eating Gluten for Tests to Work
This is the single most important thing to know before getting tested. If you’ve already cut gluten from your diet, your antibody levels will drop and your intestinal lining may start healing, which can produce a false negative on both blood tests and biopsies. The tests are measuring your body’s active immune reaction to gluten, so gluten needs to be present in your system.
If you’ve been gluten-free and want accurate results, you’ll need to do what’s called a gluten challenge: deliberately eating gluten every day before testing. Current guidance suggests consuming 3 to 6 grams of gluten per day (roughly one to two slices of wheat bread) for at least 12 weeks. If your symptoms become severe, an abbreviated challenge of 6 to 12 weeks may be acceptable, but shorter than that risks an inconclusive result. Clinical monitoring during this period is important because the dose or duration sometimes needs adjusting based on how you respond.
Intestinal Biopsy: The Confirmation Step
When blood work comes back positive, most adults are referred for an upper endoscopy. During this procedure, a gastroenterologist passes a thin, flexible tube through your mouth and into your small intestine, taking several tiny tissue samples from the lining. You’re sedated for the procedure, and it typically takes 15 to 20 minutes. The samples are then examined under a microscope.
Pathologists grade the damage using a system called the Marsh classification, which ranges from 0 to 3. A Marsh 0 result means the tissue looks normal, with no signs of immune activity. Marsh 1 shows increased immune cells in the intestinal lining but no structural damage yet. Marsh 2 adds early changes in the tissue’s architecture. Marsh 3 is where the hallmark damage of celiac disease appears: the tiny finger-like projections (villi) that line your small intestine and absorb nutrients become flattened. This stage is further divided into mild, moderate, and total villous atrophy. A Marsh 3 result, combined with positive blood work, confirms celiac disease.
Genetic Testing: Ruling Celiac Disease Out
Genetic testing for celiac disease looks for two gene variants called HLA-DQ2 and HLA-DQ8. About 30% to 40% of the general population carries one of these genes, so having them doesn’t mean you have celiac disease. But if you don’t carry either gene, you can essentially rule celiac disease out. The test has a poor positive predictive value but a very high negative predictive value.
This makes genetic testing most useful in specific situations. If you’ve already gone gluten-free before getting tested and don’t want to do a 12-week gluten challenge, a negative genetic test can save you that process entirely. It’s also helpful when blood work or biopsy results are ambiguous, or for screening family members of someone with confirmed celiac disease. The test itself is a simple blood draw or cheek swab and only needs to be done once in your lifetime, since your genes don’t change.
Home Test Kits: What They Can and Can’t Do
Several at-home celiac screening kits are now available. These use a finger-prick blood sample to detect the same tTG or EMA antibodies that lab tests measure. In clinical settings where trained nurses administered rapid finger-prick tests, sensitivity dropped to about 78% compared with the 90% to 95% seen in standard lab testing. There is very little data on how well these tests perform when administered by the general public at home.
A home test can be a reasonable first step if you’re unsure whether to pursue further evaluation, but a negative result doesn’t rule out celiac disease. And a positive result still needs to be confirmed through standard lab testing and likely a biopsy. These kits should be treated as a screening tool, not a diagnosis.
Testing for Non-Celiac Gluten Sensitivity
Non-celiac gluten sensitivity is a different situation entirely. There is no blood marker or biopsy finding that identifies it. The diagnosis is made by exclusion: first, celiac disease must be ruled out through the blood tests and possibly biopsy described above. Wheat allergy also needs to be ruled out, typically through skin prick testing or specific IgE blood tests.
Once both are negative, the formal diagnostic protocol involves a structured elimination and reintroduction process. You start by following a strict gluten-free diet for at least four weeks, eliminating even trace amounts of gluten. If your symptoms improve significantly during this period, the next step is a blinded challenge: you consume either gluten (8 grams per day, hidden in a food like a muffin or bar) or an identical gluten-free placebo for one week, followed by a one-week washout period of eating gluten-free again, then switch to whichever one you didn’t have the first time. You track your symptoms daily with a standardized questionnaire throughout.
A positive result requires at least a 30% worsening of your one to three main symptoms during the gluten week compared to the placebo week. This double-blind crossover approach, established by an international panel of experts in Salerno, Italy, exists because gluten sensitivity symptoms overlap heavily with other conditions, and the placebo effect is strong. In practice, most doctors use a simplified version of this protocol, but the core principle remains: your symptoms need to clearly worsen with gluten and improve without it, after celiac disease and wheat allergy have been excluded.
Which Tests to Start With
If you suspect gluten is causing your symptoms, the most efficient path is to keep eating gluten and ask your doctor for a tTG-IgA blood test. If you have a condition that lowers your IgA levels (about 2% to 3% of people with celiac disease do), your doctor can order an IgG-based version of the test instead. From there, results guide the next step: biopsy for positive results, genetic testing for ambiguous ones, and an elimination protocol if celiac disease is ruled out but you still suspect gluten sensitivity.
The key timing detail worth repeating: do not stop eating gluten before your initial testing. Starting a gluten-free diet before getting blood work is the most common reason for missed or delayed diagnoses, and going back on gluten for 12 weeks after you’ve felt better can be genuinely miserable. Getting tested while you’re still eating gluten saves you that step entirely.