Lab result explainedInflammationLast updated November 10, 2026

tTG-IgA celiac blood test: normal range, weak positive and high results explained

Tissue transglutaminase IgA (celiac test) (tTG-IgA) · Celiac disease serology (tTG-IgA with total IgA; sometimes DGP-IgG and EMA-IgA) · reported in U/mL (also reported as AU/mL, RU/mL or an index); interpretation is by multiples of the laboratory's upper limit of normal

Tissue transglutaminase IgA (tTG-IgA) is the antibody test used first when celiac disease is suspected, and in most people it is what "the celiac blood test" means. Tissue transglutaminase is an enzyme in the gut lining that modifies gluten fragments; in celiac disease the immune system makes IgA antibodies against the enzyme itself, and their level in blood tracks the damage to the small intestine. On the most widely used assays a result under about 4 U/mL is negative, 4 to 10 is weak positive and above 10 is positive, though other assays use cut-offs of 7, 15 or 20 U/mL, so the reference range on your report is the one that applies.

Two conditions have to be met for the result to mean anything. First, you must be eating gluten: the antibodies fall within weeks of starting a gluten-free diet and a test done after cutting gluten out can be falsely normal. Second, your total IgA must be measured alongside, because about 1 in 40 people with celiac disease (and 1 in 400 to 500 of everyone) cannot make IgA at all, and in them the tTG-IgA will read as negative no matter how severe the disease. When total IgA is low, the IgG-based tests (tTG-IgG or deamidated gliadin peptide IgG) take over.

tTG-IgA is a screening test with a sensitivity and specificity both around 95 percent in people eating gluten. A strongly positive result, more than 10 times the upper limit of normal, has a positive predictive value above 99 percent for intestinal damage and in children is now accepted as diagnostic without a biopsy when confirmed by a positive endomysial antibody on a second blood sample. A weak positive is more ambiguous: fewer than half of people with low-titer results turn out to have celiac disease, and other autoimmune and liver conditions can produce them, so those results lead to further antibody testing and usually an endoscopy with duodenal biopsies.

tTG-IgA at a glance

  • What it is: IgA antibodies against tissue transglutaminase, the enzyme targeted by the immune response in celiac disease; the first-line blood test for celiac disease in anyone over 2 years old.
  • Normal: below about 4 U/mL on common assays (others use below 7, 15 or 20 U/mL). Weak positive: roughly 4 to 10 U/mL (or 20 to 30 on a 20-cut-off assay). Positive: above 10 (or above 30). Labs differ; use the cut-off on your report.
  • Strongly positive: more than 10 times the upper limit (above about 40 U/mL on a 4-cut-off assay) has a positive predictive value over 99 percent for villous atrophy.
  • The test is only valid while you are eating gluten (at least the equivalent of 1 to 2 slices of bread a day for 6 to 8 weeks) and only interpretable if your total IgA is normal.
  • A weak positive is confirmed with endomysial antibody (EMA-IgA) and usually a duodenal biopsy; false positives occur in type 1 diabetes, autoimmune thyroid and liver disease, heart failure and other conditions.
  • Next step after a positive result: referral to gastroenterology for endoscopy and biopsy before changing your diet; after diagnosis, tTG-IgA is repeated at 6 to 12 months to confirm it is falling on a gluten-free diet.

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What tTG-IgA measures

Celiac disease is an immune reaction to gluten, the storage protein of wheat, barley and rye, in people who carry the HLA-DQ2 or HLA-DQ8 genes (about 30 to 40 percent of the population, of whom around 3 percent develop the disease). Gluten is poorly digested, and its fragments are modified by tissue transglutaminase 2 (tTG2) in the gut lining, a chemical change (deamidation) that makes them bind tightly to HLA-DQ2 or DQ8 and activate T cells. The resulting inflammation flattens the finger-like villi of the small intestine, impairing absorption of iron, folate, calcium, vitamin D and fat. In the process, B cells make antibodies not only against the modified gluten fragments but against the transglutaminase enzyme that created them, and those are what the test detects.

The laboratory measures tTG-IgA by ELISA or chemiluminescence using recombinant human transglutaminase as the target; older guinea-pig-liver assays were less accurate. Results are reported in units per millilitre or arbitrary units, calibrated differently by each manufacturer, which is why cut-offs range from 4 to 20 U/mL and why guidelines express strongly positive results as multiples of the upper limit of normal rather than a fixed number. The endomysial antibody (EMA-IgA) test detects the same antibody by immunofluorescence on monkey esophagus or human umbilical cord tissue; it is nearly 100 percent specific, reported as positive or negative with a titer, and is used to confirm positive tTG results. Deamidated gliadin peptide (DGP) antibodies target the modified gluten fragments and are useful in IgA deficiency and in children under 2.

Antibody levels reflect current gluten exposure and current intestinal damage. They rise over weeks to months of eating gluten in a susceptible person and fall after gluten is removed, with roughly 80 percent of patients reaching the normal range within 12 months of a strict gluten-free diet and most of the rest within 2 years; very high starting values take longest. The test is also used in people with symptoms despite a gluten-free diet: a persistently positive tTG-IgA almost always means ongoing gluten exposure, deliberate or hidden. Total IgA (normal roughly 70 to 400 mg/dL in adults; deficiency below 7 mg/dL) must be checked once, because IgA-based tests are blind in IgA deficiency.

Normal range for tTG-IgA

Reference ranges vary between labs and by age, sex and pregnancy. Use the range printed on your own report.

GroupTypical range (U/mL (also reported as AU/mL, RU/mL or an index); interpretation is by multiples of the laboratory's upper limit of normal)Notes
NegativeBelow about 4 U/mLCommon cut-offs include 4, 7, 15 and 20 U/mL depending on the assay. Use the reference range printed on your report. Only valid if you were eating gluten and your total IgA is normal.
Weak (low) positiveAbout 4–10 U/mL (or 20–30 U/mL on a 20-cut-off assay)Positive predictive value for celiac disease is under 50 percent at this level; confirmed with EMA-IgA and biopsy. Can be caused by other autoimmune diseases, liver disease, heart failure and infections.
PositiveAbove 10 U/mL (or above 30 U/mL on a 20-cut-off assay) up to 10 times the upper limitLikely celiac disease; endoscopy with duodenal biopsies is the standard confirmation in adults.
Strongly positiveMore than 10 times the upper limit (above about 40 U/mL on a 4-cut-off assay, or above 200 on a 20-cut-off assay)Positive predictive value for villous atrophy above 99 percent. In children, a no-biopsy diagnosis is accepted if EMA-IgA is also positive on a separate sample (ESPGHAN 2020); the 2023 ACG guideline allows this option in selected adults.
Total IgA (must be measured alongside)Adults about 70–400 mg/dL; selective IgA deficiency below 7 mg/dLIgA deficiency affects 1 in 400 to 500 people and about 2 to 3 percent of people with celiac disease; in these people tTG-IgA is falsely negative and tTG-IgG or DGP-IgG is used instead.
Children under 2 yearstTG-IgA used with DGP-IgGtTG-IgA is less sensitive in the first 2 years of life; guidelines add deamidated gliadin peptide antibodies.
After 6–12 months on a gluten-free dietExpected to fall by at least half and usually into the normal rangeAround 80 percent normalize by 12 months; persistently positive levels indicate ongoing gluten exposure.
Not eating gluten before the testAny value, including negative, is uninterpretableA gluten challenge of at least 3 g of gluten a day (about 1.5 slices of bread) for 2 to 8 weeks, ideally 6 to 8 weeks, is needed before testing; the longer the better.

High (positive) tTG-IgA

A positive tTG-IgA while you are eating gluten means your immune system is making antibodies against tissue transglutaminase, and the most likely explanation is celiac disease. How confident you can be depends on the level. Above 10 times the upper limit of normal, the chance that a biopsy would show villous atrophy is over 99 percent, which is why children with a result this high and a positive endomysial antibody on a second sample can now be diagnosed without endoscopy, and why the 2023 American College of Gastroenterology guideline offers the same route to selected adults who prefer to avoid a scope. For results between the cut-off and 10 times the limit, the probability of celiac disease is high but not certain, and a duodenal biopsy remains the standard way to confirm it before committing to a lifelong gluten-free diet.

A weak positive, just above the cut-off, is the result most people find confusing. In this band fewer than half of people turn out to have celiac disease. Low-titer tTG-IgA occurs in type 1 diabetes, autoimmune thyroid disease, autoimmune hepatitis and primary biliary cholangitis, cirrhosis, heart failure, inflammatory bowel disease, psoriasis, Giardia and other infections, and sometimes for no identifiable reason. The next step is an endomysial antibody test, which is almost never positive outside celiac disease, and in most cases an endoscopy with at least four duodenal biopsies. HLA-DQ2/DQ8 typing can also help: a negative result makes celiac disease very unlikely and can close the question.

The one thing not to do with a positive result is start a gluten-free diet before the diagnosis is confirmed. Antibody levels fall and the intestinal lining heals within weeks to months of removing gluten, so a biopsy done after the diet has started can be normal, leaving you with a lifelong restriction and no clear diagnosis. If you have already cut gluten out, a supervised gluten challenge (at least 3 g a day, roughly a slice and a half of bread, for 2 to 8 weeks) is needed before the tests become reliable again. After diagnosis, the same test is your progress marker: a falling tTG-IgA at 6 and 12 months shows the diet is working, and a persistently high one means gluten is still getting in.

Common causes

  1. Celiac disease

    The cause in the great majority of clearly positive results and almost all results above 10 times the upper limit. Affects about 1 percent of the population; most people are undiagnosed. Confirmed by EMA-IgA and duodenal biopsy showing villous atrophy (Marsh 3).

  2. Dermatitis herpetiformis

    The skin form of celiac disease: intensely itchy blistering rash on the elbows, knees, buttocks and scalp. tTG-IgA is positive in 70 to 90 percent and most patients have intestinal changes even without gut symptoms; diagnosed by skin biopsy showing IgA deposits.

  3. Type 1 diabetes

    Celiac disease is 5 to 10 times more common in type 1 diabetes (about 5 percent of patients), and low-titer tTG-IgA without celiac disease also occurs; screening at diagnosis of diabetes and periodically afterwards is recommended.

  4. Autoimmune thyroid disease

    Hashimoto's thyroiditis and Graves' disease carry a 2 to 5 percent prevalence of celiac disease and a higher rate of weak-positive tTG results without it.

  5. Autoimmune and chronic liver disease

    Autoimmune hepatitis, primary biliary cholangitis, primary sclerosing cholangitis and cirrhosis of any cause can produce low-titer tTG-IgA; the antibodies usually bind transglutaminase less specifically and EMA is negative.

  6. Heart failure, inflammatory bowel disease and psoriasis

    Each is associated with weak-positive tTG-IgA in a few percent of patients without celiac disease; the mechanism is thought to be transglutaminase release from damaged tissue.

  7. Infections

    Giardia, rotavirus, other gut infections and some viral illnesses can transiently raise tTG-IgA, particularly in children; repeat testing after recovery usually shows a fall.

  8. Ongoing gluten exposure after diagnosis

    In someone already diagnosed, a tTG-IgA that stays high or rises again means gluten is still being eaten, most often through cross-contamination, oats contaminated with wheat, sauces, processed foods or medications containing gluten-based excipients.

  9. Down syndrome, Turner syndrome and Williams syndrome

    Celiac disease is 5 to 10 times more common in these genetic conditions and screening is recommended; results are interpreted the same way.

  10. First-degree relatives of people with celiac disease

    About 1 in 10 first-degree relatives has celiac disease, often without symptoms; a positive tTG-IgA in a relative is treated as probable disease and investigated.

Symptoms that can go with it

  • Often none, or only vague fatigue; many adults with celiac disease have no gut symptoms at all
  • Chronic diarrhea, bulky pale or greasy stools, bloating, excess gas and abdominal pain
  • Constipation (in about 10 percent of adults, and common in children)
  • Unexplained weight loss, or in children poor growth, delayed puberty and a swollen belly
  • Iron-deficiency anemia that does not respond to iron tablets, tiredness and breathlessness
  • Mouth ulcers, dental enamel defects, bone pain or early osteoporosis
  • An intensely itchy blistering rash on the elbows, knees or buttocks (dermatitis herpetiformis)
  • Numbness or tingling in the hands and feet, headaches, brain fog, infertility or recurrent miscarriage

Read it alongside

  • Total IgA — essential; without it a negative tTG-IgA cannot be trusted. If IgA is below the detection limit, tTG-IgG or DGP-IgG is used instead.
  • Endomysial antibody (EMA-IgA) — the confirmatory antibody test, nearly 100 percent specific; a positive EMA with a positive tTG makes celiac disease almost certain.
  • Deamidated gliadin peptide IgG (DGP-IgG) — used when total IgA is low, in children under 2, and as a second marker when tTG is borderline.
  • HLA-DQ2/DQ8 genotyping — a negative result rules celiac disease out almost completely; a positive result does not rule it in, since 30 to 40 percent of people carry these genes.
  • Ferritin, iron saturation, hemoglobin — iron deficiency is the most common presentation of adult celiac disease and should be rechecked after diagnosis.
  • Vitamin D, calcium, folate, vitamin B12 and zinc — commonly low at diagnosis because of malabsorption; a bone density scan is often advised in adults.
  • ALT and AST — mildly raised liver enzymes are found in up to 40 percent of newly diagnosed adults and usually normalize on a gluten-free diet.
  • TSH and glucose or A1C — autoimmune thyroid disease and type 1 diabetes travel with celiac disease and are screened for at diagnosis.

What usually happens next

  1. Keep eating gluten until the work-up is complete; do not start a gluten-free diet after a positive result until a gastroenterologist has confirmed the diagnosis, usually with an endoscopy and at least four duodenal biopsies.
  2. Check that your total IgA was measured; if it was not, or it is low, ask for tTG-IgG and DGP-IgG, because a negative tTG-IgA alone means nothing in IgA deficiency.
  3. For a weak positive, expect an EMA-IgA test and often HLA-DQ2/DQ8 typing before a biopsy decision; for a result more than 10 times the upper limit, ask whether a no-biopsy diagnosis is appropriate in your case.
  4. If you had already removed gluten before testing, a supervised gluten challenge (at least 3 g a day for 2 to 8 weeks, longer if tolerated) is needed before antibody tests or biopsy become reliable.
  5. After diagnosis, ask for a referral to a dietitian experienced in celiac disease, baseline ferritin, vitamin D, B12, folate, liver enzymes, thyroid function and a bone density scan, and a repeat tTG-IgA at 6 and 12 months to confirm it is falling.
  6. Suggest testing for first-degree relatives (parents, siblings, children), since about 1 in 10 will have celiac disease, often without symptoms.

Diet, lifestyle and natural levers with evidence

What can move tTG-IgA once the cause is known. Nothing here replaces finding the cause.

A strict gluten-free diet (the only treatment)

Strong evidence

Removing wheat, barley and rye completely is the treatment for celiac disease and the one lever that reliably lowers tTG-IgA. In follow-up studies, antibody levels fall by half within about 3 months and reach the normal range in roughly 80 percent of patients by 12 months, with intestinal healing in 60 to 80 percent of adults by 2 years (faster in children). Symptoms, iron levels and bone density improve in parallel. Even small regular amounts of gluten (more than about 10 to 50 mg a day, a few crumbs) can keep antibodies up and the gut inflamed.

Do not start the diet before the diagnosis is confirmed; it makes the antibody tests and biopsy unreliable. A gluten-free diet has no proven benefit for people without celiac disease or wheat allergy.

Dietitian-led education and label reading

Moderate evidence

The commonest reason for a tTG-IgA that stays positive is inadvertent gluten from cross-contamination, shared toasters and fryers, sauces, processed meats, beer and some medications. Studies of non-responsive celiac disease find hidden gluten exposure in about half of cases, and structured dietitian education improves adherence scores and antibody normalization compared with written advice alone. Certified gluten-free oats are tolerated by the large majority of people with celiac disease, but ordinary oats are frequently contaminated with wheat.

Replace the nutrients that malabsorption has depleted

Strong evidence

At diagnosis, iron deficiency is present in about a third of adults, vitamin D deficiency and low bone density in a quarter to a half, and folate, B12 and zinc deficiencies are common. Guidelines recommend measuring and correcting each one; iron stores typically recover within 6 to 12 months of a gluten-free diet plus supplementation, and bone density improves by 5 to 8 percent in the first year of treatment. Repletion treats the consequences of celiac disease rather than the antibody itself.

Iron supplements can cause constipation and should be dosed to a ferritin target rather than taken indefinitely; vitamin D doses should be guided by a blood level.

Timing the test correctly: stay on gluten

Strong evidence

A reliable tTG-IgA needs gluten in the diet. In a gluten-challenge study of adults with known celiac disease, 3 g of gluten a day for 2 weeks produced measurable intestinal changes in most participants but antibody rises in fewer than half, whereas 6 to 8 weeks of at least 3 to 10 g a day (1.5 to 5 slices of bread) raises antibodies in most. If you have been gluten-free for months, expect a challenge of at least 6 weeks before testing, and tell the clinician if symptoms become severe so the challenge can be shortened and a biopsy arranged.

Probiotics for persistent symptoms on a gluten-free diet

Preliminary evidence

In a randomised trial of 109 people with celiac disease and irritable-bowel-type symptoms despite a strict gluten-free diet, a mixture of Lactobacillus and Bifidobacterium strains for 6 weeks improved symptom scores more than placebo. Probiotics do not lower tTG-IgA, do not protect against gluten and are not a substitute for the diet; they may help residual bloating and bowel symptoms in some people.

When to see a clinician promptly

  • Severe diarrhea with dehydration, dizziness or inability to keep fluids down, or black or bloody stools, which need same-day assessment whatever the antibody result.
  • Unexplained weight loss, persistent abdominal pain, fever or night sweats in someone with celiac disease, particularly after years of diagnosis, since refractory disease and small-bowel lymphoma are rare but serious complications.
  • A positive tTG-IgA at any level, to arrange gastroenterology referral and biopsy before changing your diet.
  • Symptoms that persist or antibodies that stay high after 12 months on a gluten-free diet, to review the diet for hidden gluten and consider other diagnoses (microscopic colitis, lactose intolerance, pancreatic insufficiency, small intestinal bacterial overgrowth).
  • A child with poor growth, a swollen abdomen, chronic diarrhea or irritability, or an adult with iron-deficiency anemia that does not respond to iron, both of which warrant celiac testing.
  • An intensely itchy blistering rash on the elbows, knees or buttocks, which may be dermatitis herpetiformis and is diagnosed by skin biopsy.

Frequently asked questions

What is the normal range for tissue transglutaminase IgA?

On the most common assays, a tTG-IgA under 4 U/mL is negative, 4 to 10 is weak positive and above 10 is positive. Other manufacturers use cut-offs of 7, 15 or 20 U/mL, so the number by itself can mislead; what matters is where your result sits relative to the upper limit on your report, and whether you were eating gluten and have a normal total IgA when the sample was taken.

What does a weak positive tTG-IgA mean?

A result just above the cut-off (for example 5 to 10 U/mL on a 4-cut-off assay) means celiac antibodies were detected at a low level. Fewer than half of people with a weak positive have celiac disease; the rest have a low-level result from type 1 diabetes, autoimmune thyroid or liver disease, heart failure, an infection or no identifiable cause. The next step is an endomysial antibody test, HLA-DQ2/DQ8 typing in some cases, and usually a duodenal biopsy. Keep eating gluten until this is done.

What does a high tTG-IgA mean?

A tTG-IgA more than 10 times the upper limit of normal (above about 40 U/mL on a 4-cut-off assay, or above 200 on a 20-cut-off assay) is strongly positive, and over 99 percent of people with results this high have villous atrophy on biopsy. In children, a positive endomysial antibody on a second sample allows a diagnosis without endoscopy; in adults the 2023 ACG guideline permits this in selected cases, though biopsy remains standard. Values of several hundred are common at diagnosis and fall over 1 to 2 years on a gluten-free diet.

Do I need to be eating gluten for the celiac blood test?

Yes. The antibodies are made in response to gluten and fall within weeks of removing it, so a test done on a gluten-free or low-gluten diet can be falsely negative. Guidelines advise eating gluten daily, at least 3 g (about 1.5 slices of wheat bread) and ideally more, for 6 to 8 weeks before testing. If you have already gone gluten-free, discuss a supervised gluten challenge with your clinician rather than testing straight away.

Why is total IgA tested with tTG-IgA?

Because tTG-IgA relies on your ability to make IgA antibodies. Selective IgA deficiency affects about 1 in 400 to 500 people in general and 2 to 3 percent of people with celiac disease, and in these people the tTG-IgA is negative however severe the disease. Measuring total IgA once identifies them so that IgG-based tests (tTG-IgG or deamidated gliadin peptide IgG) can be used instead.

Can tTG-IgA be positive without celiac disease?

Yes, usually at low titer. Weak-positive results occur in type 1 diabetes, Hashimoto's and Graves' disease, autoimmune hepatitis, primary biliary cholangitis, cirrhosis, heart failure, inflammatory bowel disease, psoriasis and after gut infections such as Giardia. Strongly positive results (over 10 times the limit) are almost always celiac disease. The endomysial antibody test is the usual way to separate true from false positives, because it is rarely positive in anything else.

Can I have celiac disease with a negative tTG-IgA?

Yes, in a few situations: if you were not eating enough gluten before the test, if you are IgA deficient, in children under 2 (where DGP-IgG is added), on immunosuppressive drugs, and in a small number of people with genuine seronegative celiac disease (about 5 to 10 percent of cases, more often older adults with milder villous damage). If symptoms strongly suggest celiac disease despite a negative test, a gastroenterologist may still recommend biopsy.

How long does it take for tTG-IgA to go down on a gluten-free diet?

Levels typically halve within about 3 months and reach the normal range in around 80 percent of people by 12 months, though very high starting values can take 2 years or more. The usual plan is a repeat test at 6 and 12 months. A level that is falling confirms the diet is working; one that plateaus above normal or rises again almost always means gluten is still getting in, and a dietitian review is the next step rather than more tests.

References

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  2. Celiac disease: diagnosis and treatment. Mayo Clinic (2023)View source
  3. Diagnosis of celiac disease. National Institute of Diabetes and Digestive and Kidney Diseases (2024)View source
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  6. Werkstetter KJ, Korponay-Szabó IR, Popp A, et al.. Accuracy in diagnosis of celiac disease without biopsies in clinical practice. Gastroenterology (2017)
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This page is educational and is not medical advice or a diagnosis. Lab results have to be interpreted together with your history, symptoms and other results by a clinician who knows you. Do not start or stop a supplement to change a lab value before the cause is known.