Celiac disease: symptoms, the tTG-IgA blood test, and what your result means

Celiac disease is an autoimmune condition, meaning the immune system attacks the body's own tissue, triggered by gluten, the main protein in wheat, barley and rye. In people with celiac disease, eating gluten sets off an immune reaction that damages the small intestine's lining and makes it harder to absorb iron, folate, vitamin D and other nutrients. ¹⁵ It is diagnosed with a blood test for tTG-IgA (tissue transglutaminase IgA antibodies) plus a total IgA level, and in adults it is confirmed with small biopsies taken during an upper endoscopy, a camera test down the throat. ¹⁴ The treatment is a strict, lifelong gluten-free diet. ¹ What to do next: if you suspect celiac disease, ask your clinician about a tTG-IgA with total IgA before changing your diet, because going gluten-free first can make the test falsely negative. ²

What is celiac disease?

The ACG defines celiac disease as "a permanent immune-mediated response to gluten present in wheat, barley, and rye." ¹ When someone with celiac disease eats gluten, the immune system makes antibodies, including antibodies against tissue transglutaminase, an enzyme in the gut lining. The reaction flattens the villi, the tiny finger-like folds that give the small intestine its huge absorbing surface. ¹ With fewer villi, less iron, folate, calcium, vitamin D and other nutrients get through, which is why so many people with celiac disease are first noticed through a lab result rather than a stomach ache. ⁵⁸

Who gets celiac disease, and how common is it?

About 1% of people worldwide have celiac disease, around 2 million people in the United States. ⁵ A 2018 review of 96 studies put the global rate at 1.4% by blood test and 0.7% when biopsy confirmation was required, with higher rates in children than adults (0.9% vs 0.5%) and in females than males (0.6% vs 0.4%). ¹¹ Many people with celiac disease have never been diagnosed, partly because the symptoms are so varied.

Genes set the stage. Celiac disease almost always occurs in people with the HLA-DQ2 or HLA-DQ8 gene variants; about 30% of people carry one, but only about 3% of those carriers develop the disease. ⁶ Other things raise the odds: a family member with celiac disease, being female, and having Down, Turner or Williams syndrome. ⁵ Celiac disease also travels with other immune conditions. NIDDK lists type 1 diabetes, thyroid disease such as Hashimoto's disease and Graves' disease, Addison's disease, autoimmune liver disease, Sjögren's syndrome and selective IgA deficiency among the conditions people with celiac disease often also have. ⁵ The autoimmune hub groups these together.

Left untreated, celiac disease can lead to bone thinning and softening, anemia, malnutrition, nerve problems and fertility problems; rarely, it leads to small intestine cancer, serious liver damage or non-Hodgkin lymphoma. ⁵ People with no symptoms can still develop these complications, which is the main reason a positive result is followed up even in someone who feels well. ⁶

How celiac disease is diagnosed: blood tests first, then a biopsy

The ACG guideline describes a two-step diagnosis. CD-specific antibodies in the blood, especially tissue transglutaminase, are "very helpful for the initial screening," and "intestinal biopsy is required in most patients to confirm the diagnosis." ¹ The first blood tests are tTG-IgA and total IgA together. ⁴ If they are positive, a gastroenterologist usually performs an upper endoscopy and takes four or more biopsies, because the damage can be patchy. ⁴ A pathologist then looks at the samples under a microscope for flattened villi and extra immune cells, graded on a scale called the Marsh classification. ²⁷

In children, the rules differ. ESPGHAN, the European pediatric gastroenterology society, allows a diagnosis without biopsy when tTG-IgA is at least 10 times the upper limit of normal, endomysial antibodies are positive on a second blood sample, and the family agrees; below that level, at least four biopsies from the lower duodenum and one from the duodenal bulb are taken. ³ The ACG suggests a no-biopsy strategy only "in selected children." ¹ For adults, the AGA notes that a tTG-IgA over 10 times the upper limit with a positive EMA has a positive predictive value of "virtually 100%," but an endoscopy may still be done to look for other problems. ²

Keep eating gluten until testing is finished

This is the step people most often get wrong. The AGA's practice update states: "Reduction or avoidance of gluten before diagnostic testing is discouraged, as it may reduce the sensitivity of both serology and biopsy testing." ² MedlinePlus advises continuing to eat foods with gluten for a few weeks before testing, and NIDDK says doctors do not recommend starting a gluten-free diet before diagnostic testing. ⁷⁹ A negative tTG-IgA in someone who had already cut out most gluten does not rule celiac disease out.

Why total IgA is ordered with tTG-IgA

IgA (immunoglobulin A) is the antibody class that guards the lining of the gut, and tTG-IgA is an IgA antibody. A person with selective IgA deficiency makes little or no IgA, so tTG-IgA will read negative even with active celiac disease. ² Labcorp calls IgA deficiency "a relatively frequent finding in celiac disease," and NIDDK lists it among the conditions that occur alongside it. ⁵¹⁰ When total IgA is low, guidelines switch to IgG-based tests, tTG-IgG or DGP-IgG, which MedlinePlus notes are also often used for children under 2. ²⁹ The autoimmune antibodies guide explains how antibody tests are read more generally.

The markers to check with celiac disease

Beyond the antibody tests, a handful of routine labs show whether celiac disease has already affected absorption and which related conditions to look for. The ACG summary lists unexplained iron deficiency, bone thinning and thyroid disease among the reasons to consider celiac testing in the first place. ⁴ NIDDK notes that doctors may test for low vitamin and mineral levels and treat any deficiency they find. ⁸

Read the blood count first: the CBC guide explains hemoglobin, MCV and the rest of the panel. Then read the patterns together, because a combination tells you more than any single flag.

The deficiencies have their own pages: iron deficiency, anemia, vitamin D deficiency and B12 deficiency. Bone loss is covered on the osteoporosis page.

tTG-IgA 0.5, 2, 10 or 100: what the number means

tTG-IgA has no single universal scale. Labs use different test kits, so a value only makes sense against the range printed on the same report. Labcorp, for instance, lists two schemes for its test: negative under 7.0, equivocal 7.0 to 10.0 and positive above 10.0 U/mL on one, and negative 0 to 3, weak positive 4 to 10 and positive above 10 U/mL on the other. ¹⁰ Some labs report in a different unit or as an index. The lab units guide and reference ranges guide explain why.

• tTG-IgA of 0.5, 1 or 1.2 U/mL, or "less than 2": little or no antibody found; negative on Labcorp's scales. Reassuring only with a normal total IgA and gluten in the diet beforehand. ²¹⁰
• tTG-IgA of 2 or 3 U/mL: still negative on both Labcorp scales. The same two checks apply. ¹⁰
• tTG-IgA of 4 to 10 U/mL: weak positive or equivocal, depending on the scale. This is the grey zone where clinicians often repeat the test, add an endomysial antibody test, or move to biopsy based on symptoms. ²¹⁰
• tTG-IgA above 10 U/mL: positive on Labcorp's scales; in adults, the usual next step is an upper endoscopy with biopsies. ¹¹⁰
• tTG-IgA at or above 10 times the lab's upper limit (100 U/mL or more where the cutoff is 10): strongly positive. With a positive endomysial antibody on a second sample, children may be diagnosed without biopsy, and in adults the chance of celiac disease is close to certain. ²³

Conditions that look like celiac disease, and the test that tells them apart

The comparison matters for testing. Many people try a gluten-free diet, feel better, and conclude they have celiac disease or gluten sensitivity. Feeling better without gluten cannot separate the two, and by then the celiac blood test is no longer reliable. Testing first keeps the answer open: a person with celiac disease needs a stricter diet, screening of close relatives and lifelong follow-up labs, which someone with gluten sensitivity does not. ¹¹²

The gluten-free diet: how celiac disease is treated

The ACG guideline states that current treatment "requires strict adherence to a gluten-free diet (GFD) and lifelong medical follow-up," and that most patients have an excellent clinical response. ¹ Strict means removing wheat, barley and rye in all forms, including hidden sources such as malt, soy sauce brewed with wheat, and cross-contact from shared toasters and fryers. Many people notice their symptoms improve within days to weeks; the intestine takes much longer to heal. ⁴⁸ A registered dietitian who knows celiac disease can teach label reading and meal planning, which NIDDK recommends. ⁸

• Labels: in the US, a food labeled "gluten-free" must contain less than 20 parts per million of gluten, a rule in force since 2014. ¹⁴
• Oats: oats are naturally gluten-free but often contaminated, so the ACG summary recommends gluten-free oats. ⁴
• Gadgets: home gluten detection devices are not recommended because of false results. ⁴
• Eating out and travel: cross-contact is the most common source of accidental gluten; ask how food is prepared.
• The rest of the diet: a gluten-free diet can fall short on fiber and some vitamins over time, so the AGA flags long-term vitamin and fiber gaps as a possible side effect. ²

What can help, and how strong the evidence is

Supplements here are about correcting a deficiency a lab has found, chosen and monitored with a clinician, not about treating celiac disease itself. LifeFrom's education guides cover the forms and the catches: iron, vitamin D, folate and vitamin B12. Iron is a common example: absorption is often poor until the intestine heals, so ferritin is rechecked rather than assumed to be rising. Find the cause and agree on any supplement with your clinician before starting it.

Follow-up blood tests: monitoring and retesting on a gluten-free diet

After diagnosis, tTG-IgA becomes a rough gauge of how well gluten is being avoided. NIDDK notes that antibody levels usually fall to normal with treatment. ⁸ The AGA recommends repeat celiac serology at 6 and 12 months after diagnosis and yearly after that, and adds a warning: a negative result in a treated patient does not prove the intestine has healed, while persistently positive serology usually means ongoing damage and gluten exposure. ² See why a trend beats a single reading.

Healing matters beyond symptoms. The ACG summary reports that lack of mucosal healing raises the risk of lymphoma-type cancers and hip fracture, while people whose biopsy has returned to normal have the same lymphoma risk as the general population. ⁴ A follow-up biopsy is not routine for everyone, so the timing is a conversation with the gastroenterologist.

When symptoms continue on a gluten-free diet

About 20% of people still have symptoms on a gluten-free diet. ⁸ The ACG calls this nonresponsive celiac disease and recommends a systematic workup, "especially" for unintentional gluten contamination. ¹ Other causes include IBS, lactose intolerance and, rarely, refractory celiac disease, in which symptoms and intestinal damage persist despite a strict diet and which needs specialist care. ¹⁸ A rising or persistently positive tTG-IgA points toward hidden gluten. ²

Who should be tested for celiac disease

The ACG summary recommends considering celiac blood tests for people with unexplained symptoms such as chronic diarrhea or weight loss, and for findings such as unexplained iron deficiency, early bone thinning or thyroid disease. ⁴ Screening people with no symptoms in the general population is not recommended, but testing first-degree relatives, the parents, siblings and children of someone with celiac disease, can be considered. ⁴ The Celiac Disease Foundation also lists people with associated conditions, such as type 1 diabetes, as candidates for testing. ¹² A negative test in a relative is not a lifetime answer; the decision to repeat it rests with their own clinician.

Questions to ask your clinician

• Was total IgA checked with my tTG-IgA, and was it normal?
• Was I eating enough gluten before the test for the result to count?
• My tTG-IgA is in the weak positive range: should we repeat it, add an endomysial antibody test, or go to endoscopy?
• Do I need a biopsy to confirm the diagnosis, and should I keep eating gluten until then?
• Which deficiencies should we check now: ferritin, folate, B12, vitamin D, zinc?
• Should I have a bone density scan or a thyroid test?
• Should my parents, siblings or children be tested?
• Can you refer me to a dietitian who knows celiac disease?
• When will we recheck my tTG-IgA, and what result would worry you?

For related reading, the gut hub collects the digestive markers, and the CBC guide walks through the blood count that often first hints at celiac disease. If your symptoms look more like IBS and your celiac tests are negative, the IBS page covers the tests that rule out other causes.

This page is general education, not medical advice or a diagnosis. The clinician who knows your history, medicines and full results is the right person to read your tests and decide the next steps with you.

Free in LifeFromAdd the lab results you already have, and LifeFrom reads each marker next to the others it moves with, in plain language, with the sources it used. Free, on the web or in the app.

Start on the web Download the app