Finding out if you have celiac disease starts with a simple blood test, but there are a few steps involved and one critical rule: you need to be eating gluten regularly before any testing, or results can come back falsely negative. The process typically begins with your primary care doctor ordering a screening blood test, with results back in one to two weeks. Depending on those results, you may need a biopsy to confirm the diagnosis.
Signs That Should Prompt Testing
Most people think of celiac disease as a digestive problem, and it often is. Bloating, diarrhea, constipation, and stomach pain after eating gluten-containing foods are the classic red flags. But celiac disease can show up in ways that seem completely unrelated to your gut, which is why it goes undiagnosed in so many people.
Unexplained iron deficiency anemia, especially if it doesn’t improve with iron supplements, is one of the most common non-digestive signs. Others include thinning bones at an unusually young age, an intensely itchy blistering rash on the elbows, knees, or buttocks (called dermatitis herpetiformis), dental enamel defects, unexplained infertility, and tingling or numbness in the hands and feet. In children, short stature and delayed puberty can be indicators. Unexplained elevations in liver enzymes and recurring joint pain also warrant screening. If you have a first-degree relative with celiac disease, your risk is significantly higher regardless of symptoms.
The First Step: Blood Testing
The standard screening test measures an antibody called tissue transglutaminase IgA (tTG-IgA). Your immune system produces this antibody when it reacts to gluten, so elevated levels are a strong signal. The test has a sensitivity between 78% and 100% and a specificity between 90% and 100%, making it one of the more reliable screening tools in medicine. Results typically come back within one to two weeks.
Your doctor should also check your total IgA level at the same time. About 2% to 3% of people with celiac disease have an IgA deficiency, which means the standard tTG-IgA test won’t work properly for them. It will come back low or normal even if celiac disease is present. If you’re IgA deficient, your doctor can use alternative tests that measure IgG-based antibodies instead, such as IgG deamidated gliadin peptide or IgG tissue transglutaminase.
You Must 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 out of your diet, your antibody levels will drop and your intestinal lining may start to heal, making both blood tests and biopsies unreliable. You need to be actively eating gluten for testing to be accurate.
If you’ve been gluten-free and want to get tested, you’ll need to do what’s called a gluten challenge. The traditional approach involves eating the equivalent of about four to six slices of bread per day (8 to 10 grams of gluten) for six to eight weeks before testing. A modified version, which is easier to tolerate, reduces that to about one and a half slices of bread per day (3 grams of gluten) and has been shown to produce reliable results. This is uncomfortable if gluten makes you feel terrible, but it’s necessary for an accurate diagnosis.
Confirming the Diagnosis With a Biopsy
A positive blood test alone doesn’t confirm celiac disease in most adults. The next step is usually an upper endoscopy, where a gastroenterologist passes a thin, flexible tube through your mouth and into your small intestine to take small tissue samples. The procedure itself is quick, typically under 30 minutes, and you’re sedated for it. You won’t feel pain during the procedure, though you may have a mild sore throat afterward.
A pathologist examines the tissue samples and grades the damage using a system called the Modified Marsh Score, which ranges from stage 0 (normal) through stages 1, 2, and up to 3a, 3b, or 3c. Most doctors diagnose celiac disease when the score reaches stage 3 or above, which indicates significant flattening of the finger-like projections (villi) that line your small intestine and absorb nutrients.
When a Biopsy Might Not Be Needed
In children, well-established guidelines now allow a diagnosis without a biopsy under specific conditions. If a child’s tTG-IgA level is at least 10 times the upper limit of normal, and a second blood sample confirms positive endomysial antibodies (a different, highly specific antibody test), the diagnosis is considered reliable without endoscopy. This applies whether the child has symptoms or not.
For adults, the path is less settled. The American College of Gastroenterology has acknowledged that the same criteria (tTG-IgA at 10 times or more the upper limit of normal, plus positive endomysial antibodies on a second sample) may be considered for symptomatic adults who are unwilling or unable to undergo endoscopy. However, most gastroenterologists still prefer biopsy confirmation in adults because other conditions can occasionally mimic celiac disease.
Genetic Testing: Useful for Ruling It Out
Genetic testing looks for two specific gene variants called HLA-DQ2 and HLA-DQ8. Over 90% of people with celiac disease carry DQ2, and another 5% to 10% carry DQ8. The real power of this test is its ability to rule celiac disease out: if you carry neither gene, there’s a greater than 98% chance you don’t have and won’t develop celiac disease.
Carrying one of these genes, however, doesn’t mean you have celiac disease. Roughly 30% to 40% of the general population carries DQ2 or DQ8, and most of them will never develop the condition. Genetic testing is most useful in specific situations: if you’ve already gone gluten-free before being tested and don’t want to do a gluten challenge, a negative genetic test can effectively take celiac disease off the table. It’s also helpful for screening family members of someone already diagnosed.
What the Testing Process Looks Like in Practice
For most people, the process follows a predictable sequence. You see your doctor, they order the tTG-IgA blood test (along with a total IgA level), and you get results in one to two weeks. If your blood test is positive, you’re referred to a gastroenterologist for an endoscopy. The wait for that appointment varies, but you should continue eating gluten until the biopsy is done. If the biopsy confirms damage consistent with celiac disease, you have your diagnosis and can begin a gluten-free diet with guidance from your care team.
If your blood test is negative but your symptoms are persistent and suggestive, your doctor may still consider further evaluation. The blood test, while very good, isn’t perfect. Some people with milder intestinal damage or early-stage disease can have normal antibody levels. In these cases, genetic testing or even a biopsy despite negative serology may be appropriate, particularly if you have a strong family history or one of the non-digestive signs described above.
One important note: home celiac tests are available over the counter, but they only check for tTG-IgA and can’t measure total IgA or perform the confirmatory steps that make a clinical diagnosis reliable. They may be a reasonable starting point if you’re unsure whether to see a doctor, but a positive or negative home test should always be followed up with proper medical evaluation.