tTG IgA Test · Blood

If you have unexplained bloating, chronic fatigue, iron deficiency that keeps coming back, or a family member with celiac disease, this is the test that answers the question standard bloodwork cannot: is gluten quietly destroying your small intestine? Celiac disease affects roughly 1 in 100 people, yet the majority remain undiagnosed because routine lab panels do not include this marker.

tTG IgA (tissue transglutaminase immunoglobulin A) measures a specific autoantibody, a self-attacking immune protein, directed against an enzyme called tissue transglutaminase 2. This enzyme normally helps repair the lining of your small intestine. In people with celiac disease, eating gluten triggers the immune system to produce antibodies that target this enzyme, and the resulting attack damages the finger-like projections (villi) that absorb nutrients from food. The higher your tTG IgA level, the more aggressive that immune attack tends to be.

How This Test Works as a Celiac Detector

In people who are eating gluten and have untreated celiac disease, tTG IgA catches roughly 95 to 98 out of every 100 true cases, with a similarly high rate of correctly clearing people who do not have the condition. That combination of sensitivity (the ability to detect true cases) and specificity (the ability to correctly clear people without the disease) makes it the recommended first-line blood test for celiac disease in every major gastroenterology guideline.

When the result is very high, at 10 times or more above the upper limit of normal (ULN) for the lab's assay, the probability of biopsy-confirmed celiac disease approaches 99 to 100%. In children, and increasingly in adults, this level of elevation can support a diagnosis without requiring an intestinal biopsy at all. A large validation study of 898 children found that the tTG IgA-based no-biopsy strategy had a positive predictive value, meaning 98.8% of those the test flagged truly had celiac disease, and a negative predictive value of 0.958, meaning 95.8% of those cleared truly did not. A combined analysis of 18 adult studies confirmed that levels at or above 10 times the ULN had 100% specificity for celiac-pattern intestinal damage.

At lower levels of positivity, between 1 and 10 times the ULN, the picture is less clear-cut. A study of 311 adults found that even low-positive and borderline-negative results frequently turned out to be celiac disease or an early stage of the condition. This means a mildly elevated result deserves investigation, not dismissal.

Mortality and Long-Term Risk

The KORA/MONICA cohort study followed 4,633 German adults for about 9 years and found that people with elevated tTG IgA had roughly twice the risk of dying from any cause compared to those with normal levels. The risk was especially pronounced in women, who had about four times the mortality risk, and cancer-related deaths were disproportionately elevated, with women showing about six and a half times higher cancer mortality. These findings were adjusted for age but not for other standard risk factors like smoking or BMI, so the numbers should be interpreted with caution. Still, they suggest that untreated celiac autoimmunity is not a benign condition you can safely ignore.

Pregnancy and Infant Health

A cohort study of 1,768 pregnant women found that those who tested positive for tTG IgA during pregnancy had about 2.6 times the odds of developing two or more celiac-related health problems, about 2.9 times the odds of a low placental-to-birth-weight ratio, and about 2.3 times the odds of poor infant weight gain in the first year. These associations held after adjusting for age, race, number of previous pregnancies, BMI, and stage of pregnancy. If you are pregnant or planning to become pregnant and have any risk factors for celiac disease, this test could reveal a treatable condition affecting both you and your baby.

The IgA Deficiency Trap

About 1 in 400 to 1 in 600 people have selective IgA deficiency, meaning their body produces very little of the IgA antibody class. Because this test specifically measures the IgA version of the anti-transglutaminase antibody, a person with IgA deficiency will get a falsely negative result even if they have active celiac disease. This is why guidelines recommend ordering total IgA alongside tTG IgA. If your total IgA is very low, your doctor should switch to IgG-based tests, such as IgG anti-tissue transglutaminase or IgG deamidated gliadin peptide (DGP), which have sensitivities around 90 to 99% in IgA-deficient patients.

Monitoring on a Gluten-Free Diet: What This Test Can and Cannot Tell You

Once celiac disease is diagnosed, tTG IgA becomes the primary monitoring tool. Levels typically drop substantially after starting a strict gluten-free diet. In a prospective study of 345 children, the average tTG IgA fell about 14-fold within three months, though most children still remained above the upper limit of normal at that point. Full normalization can take 6 to 24 months depending on how high the starting level was and the specific lab assay used.

Persistently elevated tTG IgA on a gluten-free diet is a strong signal that gluten is still getting in, whether from cross-contamination, hidden sources, or intentional dietary lapses. A study of adults with long-standing celiac disease found that 46% of those who admitted dietary deviations had elevated tTG IgA, compared to 28% of those who reported strict adherence.

Here is the limitation you need to understand: a normal tTG IgA does not guarantee your intestine has healed. A combined analysis of multiple studies found that tTG IgA catches only about 50% of people who still have persistent villous atrophy (ongoing intestinal damage) despite following a gluten-free diet. In other words, your number can look fine while your gut lining is still damaged. One study of 402 treated patients found that truly undetectable tTG IgA (below 1.2 U/mL, not just below the standard cutoff) was a stronger predictor of actual mucosal healing, meaning full repair of the intestinal lining, than low-but-detectable negative values. If you have ongoing symptoms despite a normal tTG IgA, a follow-up biopsy may still be warranted.

Reference Ranges

All tTG IgA cutoffs are specific to the assay your lab uses. The numbers below are expressed as multiples of your lab's upper limit of normal (ULN), which is the standard way guidelines define risk tiers. Your lab report will show an absolute number in units per milliliter (U/mL) or comparable units, along with the reference range for that specific assay. Do not compare your number directly to someone tested at a different lab.

Compare your results within the same lab over time for the most meaningful trend. Different testing platforms can produce meaningfully different numbers on the same blood sample, and normalization speed after starting a gluten-free diet varies by assay type.

When Results Can Be Misleading

The most common reason for a false negative is that you stopped eating gluten before the test. Even a few weeks of reduced gluten intake can lower tTG IgA enough to produce a negative result. You must be eating gluten regularly, the equivalent of at least one to two slices of bread per day for several weeks, for the test to be reliable.

IgA deficiency, as described above, is the second major cause of false negatives. Very young children under two years old can also have false-negative tTG IgA results, which is why adding DGP IgG (deamidated gliadin peptide, IgG class) improves detection in this age group.

False positives are uncommon with modern assays but can occur in people with liver disease, heavy alcohol use, type 1 diabetes, or other autoimmune conditions. One large study found that the positive predictive value of tTG IgA was lower in children with type 1 diabetes than in the general pediatric population, meaning more false positives. In a study of 948 children with juvenile arthritis, tTG IgA positivity was no higher than in healthy controls, so autoimmune disease alone does not reliably push this number up. Different commercial assays also produce different numerical values on the same sample, which means comparing results across labs can be misleading.

Tracking Your Trend

A single tTG IgA reading is useful for screening, but the real value emerges when you track it over time. If you have been diagnosed with celiac disease and started a gluten-free diet, the trajectory of your tTG IgA tells you whether your immune system is calming down. A steadily falling number is reassuring. A number that plateaus or rises after initial improvement is a signal to investigate gluten exposure more carefully.

For newly diagnosed celiac disease, get a baseline at diagnosis, retest at 3 to 6 months after starting a gluten-free diet, then at least every 6 to 12 months until the level normalizes. After that, annual monitoring is reasonable. For screening purposes, if your first test is negative and you have ongoing risk factors (family history, type 1 diabetes, persistent symptoms), retesting in 1 to 2 years is appropriate because celiac autoimmunity can appear suddenly at any age.

A study of at-risk children in the CDGEMM cohort found that tTG IgA elevation was a sudden event whose trajectory could not be predicted in advance. This means you cannot assume a negative result today will stay negative forever if you have risk factors.

What to Do with an Abnormal Result

If your tTG IgA comes back positive, the next steps depend on how high it is. At 10 times or more the ULN, especially if confirmed by a positive EMA (endomysial antibody) test, many gastroenterologists will diagnose celiac disease without a biopsy. Below that threshold, a duodenal biopsy, a small tissue sample taken from the first part of the small intestine using a flexible camera passed through the mouth, remains the standard for confirming the diagnosis.

Alongside the tTG IgA, you should have total IgA measured (to rule out IgA deficiency), and your physician may order a complete blood count, iron studies, vitamin D, vitamin B12, folate, and liver enzymes, because celiac disease commonly causes deficiencies and liver inflammation that standard panels may have already caught without connecting them to a gut problem. If the diagnosis is confirmed, a referral to a gastroenterologist and a dietitian experienced with celiac disease is the standard path. The treatment, a strict lifelong gluten-free diet, is straightforward in concept but demanding in practice.

If your tTG IgA is negative but you have strong clinical suspicion (ongoing symptoms, family history, associated conditions), check your total IgA to rule out deficiency, consider adding DGP IgG testing, and discuss whether a biopsy is warranted. A negative blood test does not always mean a clear gut.