Coeliac Disease Blood Tests: tTG, EMA & Getting Tested at Home

Key Takeaways

Coeliac disease affects around 1 in 100 people in the UK, but most remain undiagnosed.
You must be eating gluten regularly for at least 6 weeks before testing — a gluten-free diet will cause false negative results.
The first-line blood test is tTG-IgA (tissue transglutaminase antibody).
A positive blood test usually requires confirmation with a small bowel biopsy.

What Is Coeliac Disease?

Coeliac disease is an autoimmune condition in which the immune system attacks the lining of the small intestine when gluten is consumed. Gluten is a protein found in wheat, barley, and rye. The resulting damage to the intestinal villi (finger-like projections that absorb nutrients) leads to malabsorption, nutritional deficiencies, and a wide range of symptoms.

According to Coeliac UK, around 1 in 100 people in the UK have coeliac disease, but only about 36% are currently diagnosed. The average time from symptom onset to diagnosis is 13 years. Blood testing is a critical first step in identifying the condition.

The Gluten Challenge: Why You Must Be Eating Gluten

This is the single most important thing to understand about coeliac testing: you must be eating gluten regularly for at least 6 weeks before your blood test. NICE guidelines recommend consuming gluten in more than one meal every day during this period. If you have already started a gluten-free diet before being tested, the antibody levels may have dropped to normal, producing a false negative result.

If you have been gluten-free for some time, speak with your GP about a “gluten challenge” before testing. This involves reintroducing gluten into your diet for a minimum of 6 weeks prior to the blood test.

tTG-IgA (Tissue Transglutaminase Antibody)

The tTG-IgA test is the recommended first-line serological test for coeliac disease according to NICE (NG20). Tissue transglutaminase is an enzyme found in the gut lining. In coeliac disease, the immune system produces IgA antibodies against this enzyme. The test has a sensitivity of approximately 95% and a specificity of around 97%, making it highly accurate.

A positive tTG-IgA result strongly suggests coeliac disease, but does not confirm it on its own. Your GP will refer you to a gastroenterologist for further evaluation, which typically includes a duodenal biopsy.

EMA (Endomysial Antibody)

The EMA test detects IgA antibodies against endomysium, a connective tissue surrounding muscle fibres. It is highly specific for coeliac disease (close to 100%) but slightly less sensitive than tTG-IgA. It is often used as a confirmatory test when tTG-IgA is positive, or in cases where the diagnosis is uncertain.

Total IgA

Approximately 2–3% of people with coeliac disease have selective IgA deficiency. This means they produce very little IgA antibody, which would cause both the tTG-IgA and EMA tests to return falsely negative results. For this reason, total IgA should be measured alongside tTG-IgA. If total IgA is low, IgG-based tests (tTG-IgG or deamidated gliadin peptide IgG) should be requested instead.

The NICE Referral Pathway

NICE recommends the following pathway for adults:

Step 1: Request tTG-IgA and total IgA while the patient is eating gluten.
Step 2: If tTG-IgA is positive, refer to gastroenterology for duodenal biopsy.
Step 3: Continue eating gluten until the biopsy is performed.
Step 4: Biopsy confirms villous atrophy (Marsh 3 classification) — diagnosis confirmed.

In children, NICE and ESPGHAN guidelines allow a no-biopsy diagnosis if tTG-IgA is more than 10 times the upper limit of normal and EMA is positive on a separate blood sample. This pathway is not yet standard for adults in the UK.

Who Should Be Tested?

NICE recommends testing for coeliac disease in anyone with:

Chronic or intermittent diarrhoea
Unexplained iron deficiency anaemia
Unexplained weight loss or failure to thrive
Persistent abdominal pain or bloating
Recurrent mouth ulcers
Unexplained B12 or folate deficiency
Dermatitis herpetiformis (a blistering skin rash)
Type 1 diabetes (higher risk)
Autoimmune thyroid disease
First-degree relatives of someone with coeliac disease

Monitoring After Diagnosis

Once diagnosed, the treatment for coeliac disease is a strict, lifelong gluten-free diet. Monitoring blood tests are important to assess dietary adherence and nutritional recovery:

tTG-IgA — should decline and eventually normalise on a gluten-free diet. A persistently raised level suggests ongoing gluten exposure.
FBC and ferritin — to monitor for resolution of anaemia.
B12 and folate — to check nutritional recovery.
Vitamin D and calcium — coeliac disease increases the risk of osteoporosis.
Liver function tests — mildly abnormal liver enzymes are common at diagnosis and usually resolve.

Annual blood tests are recommended for the first few years after diagnosis, and your GP or gastroenterologist will advise on the appropriate ongoing schedule.

Family Screening

First-degree relatives (parents, siblings, children) of someone with coeliac disease have a 1 in 10 chance of also having the condition. NICE recommends that all first-degree relatives be offered serological testing, even if they are asymptomatic. Early detection and treatment prevents long-term complications including osteoporosis, nutritional deficiencies, and a small increase in the risk of intestinal lymphoma.

Getting Tested at Home

If you suspect you may have coeliac disease — or if a family member has been diagnosed — getting tested is straightforward. A mobile phlebotomist can take a blood sample at your home for tTG-IgA, total IgA, and related tests. Remember: you must have been eating gluten regularly for at least 6 weeks before the test. Browse our home blood test options to get started.