On July 28, 2026, France’s national health authority published its first formal guidance on diagnosing celiac disease, and the medical press picked it up over the following two days. The headline change matters well beyond France: adults can now be diagnosed without an intestinal biopsy when one number on their blood work is high enough. That number is the tTG-IgA test, and it is the same test American labs run every day. Here is what the threshold means, why a second line on the report decides whether the first one can be trusted at all, and what still differs in the United States.
What changed on July 28
Celiac disease affects roughly one person in a hundred and stays undiagnosed in most of them. The reason is that the textbook presentation, chronic diarrhea and weight loss, describes only a fraction of cases. Plenty of people have no digestive complaints at all, just fatigue and an anemia that gets blamed on something else. The new French guidance responds to that gap in two ways: it widens the list of situations that should trigger a blood test, and it accepts serology alone as proof of diagnosis in adults when antibody levels are very high. Until now, that shortcut existed only for children in most of Europe. If you want the underlying condition explained first, our guide to celiac disease and gluten intolerance covers the basics; this article is about the lab report.
One test first, but two lines to read
The recommended first-line test is the IgA anti-tissue transglutaminase antibody, written tTG-IgA or anti-TG2 IgA on most reports. Panels that stack anti-gliadin, anti-endomysial and deamidated gliadin peptide antibodies up front are not recommended: they cost more and add nothing at that stage. On this, French guidance and the American College of Gastroenterology agree.
What that line never does is stand alone. It has to be paired with a total IgA measurement, for a mechanical reason: the antibody being hunted is itself an IgA. If your body makes very little IgA, and selective IgA deficiency is more common in people with celiac disease than in the general population, the test can come back negative while the disease is fully present. A negative tTG-IgA sitting next to a collapsed total IgA is not a reassuring result, it is an uninterpretable one, and it means switching to IgG-class antibodies. If both lines are not on your report, only half the question was asked, which is a useful reflex when reading any unexpected blood test result.
The gluten-free trap
The guidance is blunt about one thing that costs diagnoses every year: do not start a gluten-free diet before the diagnosis is confirmed. These antibodies are only produced in response to dietary gluten. A few weeks of avoidance is enough to drive the level down, sometimes into the normal range. The test then reads negative, the person concludes they are not celiac, and either keeps following a restrictive diet for no documented reason or goes back to gluten believing they are in the clear. NIDDK gives the same instruction for the same reason. If you have already cut gluten out and want an answer, it has to be reintroduced for several weeks before the draw, and that is a decision to make with a clinician.
Ten times the upper limit, and what it unlocks
tTG-IgA results are not read in absolute units. They are read as multiples of the laboratory’s own upper limit of normal, usually abbreviated ULN. A result at 10x ULN means ten times the ceiling of the kit your lab uses, which is why two reports with different numbers can mean exactly the same thing. That multiple is where certainty shifts.
| What the report shows | What it means | Usual next step |
|---|---|---|
| tTG-IgA negative, total IgA normal | Celiac disease is unlikely, provided you were eating gluten | Look elsewhere for the cause of symptoms |
| tTG-IgA negative, total IgA low | Uninterpretable: IgA deficiency invalidates the test | Repeat with IgG-class antibodies |
| tTG-IgA positive, below 10x ULN | Genuine suspicion, not proof | Gastroenterology referral and duodenal biopsy |
| tTG-IgA at or above 10x ULN, adult | Diagnosis without biopsy now possible in France under set criteria | Confirmation on a second sample; biopsy still standard in the US |
| tTG-IgA at or above 10x ULN, child | Biopsy-free diagnosis widely accepted | Endomysial antibodies on a second sample |
Two caveats belong here. The biopsy-free route is framed by conditions, including confirmation on a second draw and sign-off by a gastroenterologist or pediatrician; it is not a box a patient ticks alone in front of a result. And in the United States, current ACG guidance still asks for a duodenal biopsy in most adults, with the biopsy-free approach reserved for selected cases. So a high number on an American report is a strong signal and a referral, not yet a diagnosis on its own.
What recent science changes for you
This shift did not come out of nowhere. It formalizes what the international literature has been showing for several years. A large 2024 synthesis in the journal Gastroenterology pooled data on more than twelve thousand adults across fifteen countries and landed on one takeaway worth remembering. When antibody levels run past ten times the normal ceiling in someone who was already suspected of having the disease, a positive result is almost never wrong. The flip side is just as important: a lower level rules nothing out, because a substantial share of people who truly have celiac disease sit below that mark. The threshold exists to confirm quickly, not to exclude.
A European study run across fourteen centers and published in 2023 in The Lancet Gastroenterology and Hepatology adds a nuance that helps when you look at your own figure. Certainty behaves less like a switch and more like a slope. The higher the level climbs above normal, the more likely the intestinal lining is genuinely damaged. A barely positive result and a result at fifteen times normal do not tell the same story, even though both are stamped positive on the page.
Finally, a large Norwegian survey published in 2025 in the journal Gut tested more than fifty thousand adults drawn from the general population, and it explains why nobody recommends screening everyone. In people with no symptoms and no risk factor, a plain positive proved considerably less reliable than in someone whose doctor had good reason to order the test in the first place. In practical terms: the same number does not carry the same weight depending on why it was ordered. That is exactly why guidance lists specific triggers rather than blanket screening, and why the US Preventive Services Task Force has never endorsed screening the general population.
The lab findings that should raise the question
Celiac disease damages the stretch of intestine that absorbs nutrients, so it often announces itself as holes in the blood work before any digestive symptom appears. Low ferritin that resists iron supplementation, unexplained anemia on the complete blood count, a stubbornly low vitamin D, low folate or low calcium with no explanation: each of these is unremarkable on its own and becomes a signal when it persists. Celiac disease also travels with other autoimmune conditions, thyroid disease in particular, which is why positive anti-TPO antibodies or type 1 diabetes count as risk situations, and why an autoimmune panel often follows.
Glossary
- tTG-IgA: IgA antibody against tissue transglutaminase, an enzyme in the intestinal wall; produced only in the presence of gluten in predisposed people.
- Total IgA: the overall amount of immunoglobulin A in blood, measured alongside so the tTG-IgA result can be interpreted at all.
- Selective IgA deficiency: insufficient production of immunoglobulin A, which makes the first-line test falsely negative.
- 10x ULN: ten times the laboratory’s upper limit of normal, the level above which a biopsy-free diagnosis becomes possible.
- Endomysial antibodies: a second, more specific antibody used to confirm the diagnosis without biopsy, mainly in children.
- Duodenal biopsy: a tissue sample taken during upper endoscopy, long required to confirm the diagnosis.
Frequently asked questions
Is the tTG-IgA test part of routine bloodwork?
No. It has to be ordered on purpose. A standard panel covers blood counts, iron, liver and kidney markers, never celiac antibodies. If tTG-IgA does not appear on your report, the test simply was not run.
Do I need to fast for a celiac blood test?
No fasting is required. The preparation that matters is different in nature: you must keep eating gluten normally until the draw, otherwise the result carries no meaning.
Does a low positive mean I have celiac disease?
Not on its own. A positive result below the high threshold warrants a specialist opinion and, in most US practice, a duodenal biopsy to settle the question. Other conditions can push these antibodies modestly upward, and only a gastroenterologist can sort that out.
Should my children be tested if I have celiac disease?
It is a fair question to raise. First-degree relatives are among the recognized risk situations, even without symptoms. NIDDK advises blood relatives of people with celiac disease to discuss testing with their doctor, and the timing depends on age and family context.
Sources
- Haute Autorite de Sante. Maladie coeliaque: diagnostic chez l’enfant et l’adulte. Clinical practice guideline, validated July 16, 2026, published July 28, 2026. has-sante.fr
- National Institute of Diabetes and Digestive and Kidney Diseases. Diagnosis of Celiac Disease. niddk.nih.gov
- National Institute of Diabetes and Digestive and Kidney Diseases. Celiac Disease Tests, information for health care professionals. niddk.nih.gov
- MedlinePlus, National Library of Medicine. Celiac Disease Screening. medlineplus.gov
- Rubio-Tapia A, Hill ID, Semrad C, Kelly CP, Lebwohl B. American College of Gastroenterology Guidelines Update: Diagnosis and Management of Celiac Disease. American Journal of Gastroenterology, 2023;118(1):59-76 (via PubMed). pubmed.ncbi.nlm.nih.gov
- Shiha MG, Nandi N, Raju SA, et al. Accuracy of the No-Biopsy Approach for the Diagnosis of Celiac Disease in Adults: A Systematic Review and Meta-Analysis. Gastroenterology, 2024;166(4):620-630 (via PubMed). pubmed.ncbi.nlm.nih.gov – doi.org/10.1053/j.gastro.2023.12.023
- Ciacci C, Bai JC, Holmes G, et al. Serum anti-tissue transglutaminase IgA and prediction of duodenal villous atrophy in adults with suspected coeliac disease without IgA deficiency (Bi.A.CeD). The Lancet Gastroenterology and Hepatology, 2023;8(11):1005-1014 (via PubMed). pubmed.ncbi.nlm.nih.gov – doi.org/10.1016/S2468-1253(23)00205-4
- Andersen IL, Lukina P, Dyrli OT, et al. Serological screening for coeliac disease in an adult general population: the HUNT study. Gut, 2025;74(6):918-925 (via PubMed). pubmed.ncbi.nlm.nih.gov – doi.org/10.1136/gutjnl-2024-333886
Further reading
- Celiac disease and gluten intolerance, explained
- Folate deficiency: symptoms, causes and treatment
- Vitamin B12: reading your blood test result
- Calcium blood test and the bone panel
- Ferritin: what this iron marker tells you
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