A normal tissue transglutaminase IgA (tTG‑IgA) falls below your laboratory’s cut‑off — commonly reported as <4–20 U/mL, with many labs using <10 U/mL as negative. Results above the lab’s upper limit suggest possible celiac disease and require further evaluation (repeat test, check total IgA, and clinical assessment). Always interpret using the specific assay’s reference range.

The tissue transglutaminase IgA (tTG‑IgA) test detects IgA autoantibodies against tissue transglutaminase and is used to screen for and aid diagnosis of celiac disease. It’s highly sensitive and specific but may be falsely negative in IgA deficiency, so total IgA or tTG‑IgG testing may be needed. Positive results usually prompt confirmatory small‑intestinal biopsy and clinical correlation.

In untreated celiac disease, IgA anti‑tTG and anti‑endomysial antibodies are typically elevated. However, people with celiac have a higher prevalence of selective IgA deficiency, so total serum IgA can be low in some patients. Clinicians therefore check total IgA and use IgG‑based serology when IgA is deficient to avoid false‑negative results.

A positive IgA result depends on the specific test: a positive IgA antibody suggests a recent or mucosal immune response (infection, vaccination, or autoimmune activity); positive anti‑tissue transglutaminase (tTG) IgA suggests celiac disease; elevated total serum IgA can accompany chronic infection, liver disease, or autoimmune disorders; IgA deposits in the kidney indicate IgA nephropathy. Clinical correlation and follow‑up testing are usually needed.

Early warning signs of celiac disease include persistent diarrhea or constipation, chronic abdominal pain, bloating and excessive gas, unexplained weight loss or poor growth in children, fatigue and iron‑deficiency anemia, mouth ulcers, and delayed puberty. Some people develop an itchy, blistering skin rash (dermatitis herpetiformis), nutrient deficiencies, and neurological symptoms like numbness or “brain fog.”

If your tissue transglutaminase (tTG) antibody is high, it suggests possible celiac disease but isn’t definitive. Next steps: check total IgA, confirm with endoscopic small‑bowel biopsy (or HLA DQ2/DQ8 testing if biopsy isn’t possible), and assess symptoms and nutrition. Don’t start a gluten‑free diet before confirmatory testing. Other conditions can cause false positives, so follow up with a gastroenterologist.