Get tested
the right way.

Step 1 — Blood test

It starts with a simple blood test.

The first-line test is tTG-IgA (tissue transglutaminase IgA antibody). It's the preferred screening test for most people, with a sensitivity of roughly 78–100% and specificity of 90–100% when done correctly.¹ Your doctor should also check total IgA at the same time — some people are IgA-deficient, which can make the tTG-IgA falsely negative; if so, IgG-based tests are used instead.¹²

This is often called a "celiac panel." It may also include EMA-IgA and DGP antibodies depending on the lab.⁴

Step 2 — Endoscopy

A biopsy confirms it.

If the blood test is positive, the next step is an upper GI endoscopy with biopsies of the duodenum — the small-intestine samples that show whether the villi are actually damaged. This remains the diagnostic gold standard.¹⁴ It's a short outpatient procedure, usually under light sedation.

There's one modern shortcut: if the initial tTG-IgA is very strongly positive (more than 10 times the upper limit of normal) and a second sample is EMA-positive, a confident diagnosis can sometimes be made without biopsy — but that's a decision for your specialist.¹⁵

The genetic test

HLA-DQ2/DQ8 — mainly to rule celiac out.

Nearly everyone with celiac carries the HLA-DQ2 or DQ8 genes — but so do many healthy people, so a positive result doesn't confirm celiac.² Its real value is the reverse: if you don't carry either gene, celiac becomes extremely unlikely, which is useful when the picture is unclear or you've already gone gluten-free.²

If you've already quit gluten

You may need a gluten challenge.

If you stopped eating gluten before testing, your results can come back falsely normal. Getting an accurate diagnosis then usually means a gluten challenge — going back to a gluten-containing diet (guidance often suggests the equivalent of a few slices of wheat bread daily for several weeks) before re-testing.³⁵ It's unpleasant, which is exactly why the golden rule is: test first.

What to ask your gastroenterologist

• Can we run a full celiac panel including total IgA?
• Am I still eating enough gluten for the test to be accurate?
• If serology is positive, when do we schedule the endoscopy?
• Should we baseline my iron, B12, folate, vitamin D, and bone density now?

References

Sources for this page

Every clinical claim above is numbered and traced to one of these sources. Superscript numbers in the text link here.

1. NIDDK (NIH) — Celiac Disease Tests: tTG-IgA is the preferred first-line serologic test (sensitivity 78–100%, specificity 90–100%); positive serology → duodenal biopsy to confirm. View source →
2. Serologic testing in celiac disease: a practical guide for clinicians (PMC). Measure total IgA to avoid false negatives; HLA-DQ2/DQ8 helps exclude the diagnosis. View source →
3. National Celiac Association — Diagnosing celiac disease: do not start a gluten-free diet before testing; a gluten challenge is needed if already gluten-free. View source →
4. American Gastroenterological Association — Diagnosis and monitoring of celiac disease (serology and duodenal histology; avoid reducing gluten before testing). View source →
5. AGA / NIDDK — non-biopsy route (tTG-IgA >10× ULN + positive EMA) and gluten-challenge guidance. View source →