Tissue Transglutaminase IgA (tTG) Blood Test: Normal Ranges, Causes & What Your Results Mean

What Is Tissue Transglutaminase IgA?

Tissue transglutaminase IgA (tTG-IgA) is an antibody directed against the enzyme tissue transglutaminase (tTG) — an enzyme found in the intestinal wall that plays a role in the immune response to gluten. tTG-IgA is the primary serological marker used for screening coeliac disease, with a sensitivity of 93–96% and specificity of 96–98%.

In coeliac disease, gluten peptides are deamidated by tissue transglutaminase, creating modified peptides that trigger an autoimmune response in genetically susceptible individuals (those carrying HLA-DQ2 or HLA-DQ8). This immune response damages the intestinal villi, causing malabsorption.

Why Is tTG IgA Tested?

• Coeliac disease screening — recommended first-line test by NICE and BSG guidelines
• Investigating chronic diarrhoea, bloating, or abdominal pain
• Iron deficiency anaemia — especially if unresponsive to oral iron
• Unexplained weight loss or failure to thrive in children
• Family screening — first-degree relatives of coeliac patients have 10% risk
• Associated conditions — type 1 diabetes, autoimmune thyroid disease, Down syndrome, Turner syndrome
• Dermatitis herpetiformis — the skin manifestation of coeliac disease

Normal Ranges

Important: you must be eating gluten-containing foods for at least 6 weeks before testing. A gluten-free diet will cause a false negative result.

What Does a Positive tTG IgA Mean?

• Coeliac disease — the most common interpretation; duodenal biopsy (showing villous atrophy) confirms the diagnosis
• Dermatitis herpetiformis — itchy blistering skin rash associated with coeliac disease
• False positives — possible in liver disease, heart failure, autoimmune conditions, and IgA nephropathy (usually low-titre)

What Does a Negative tTG IgA Mean?

• Coeliac disease unlikely — but cannot be completely excluded
• IgA deficiency — 2–3% of coeliac patients have selective IgA deficiency, causing false-negative tTG-IgA. Total IgA should be measured alongside tTG-IgA; if IgA is low, tTG-IgG or deamidated gliadin peptide (DGP) IgG should be used instead
• Gluten-free diet — if already avoiding gluten, the test will be falsely negative

What to Do If Positive

• Referral to gastroenterology — duodenal biopsy via endoscopy is the gold standard for diagnosis in adults
• Continue eating gluten until biopsy — stopping gluten prematurely can give a false-negative biopsy
• Lifelong gluten-free diet — the only treatment for confirmed coeliac disease
• Nutritional monitoring — check iron, folate, B12, calcium, vitamin D, and bone density at diagnosis
• Annual follow-up — tTG-IgA should normalise within 6–12 months on a gluten-free diet
• Screen family members — 10% risk in first-degree relatives

When Should You Get Tested?

• Persistent digestive symptoms (bloating, diarrhoea, constipation, abdominal pain)
• Iron deficiency anaemia not responding to iron supplements
• Unexplained fatigue, weight loss, or mouth ulcers
• Type 1 diabetes or autoimmune thyroid disease (associated conditions)
• Family history of coeliac disease
• Before starting a gluten-free diet (test first!)

Which Lola Health Tests Include tTG IgA?

tTG IgA is available as an add-on biomarker with any Lola Health blood test. For comprehensive coeliac screening, pair with total IgA to rule out IgA deficiency.