Blood Tests for Coeliac Disease
The complete guide to coeliac blood tests in Australia — which antibodies are tested, why total IgA matters, the gluten challenge rule, and what happens after a positive result.
The Coeliac Antibody Tests
Coeliac disease is diagnosed through specific antibody blood tests that detect the immune system's reaction to gluten. These antibodies are produced when the immune system attacks the intestinal lining in response to gliadin (a protein in gluten from wheat, barley, and rye).
tTG-IgA
Detects IgA antibodies against tissue transglutaminase, an enzyme found in the intestinal lining. When the immune system reacts to gluten in coeliac disease, it produces antibodies against tTG.
Role: The gold-standard first-line screening test for coeliac disease worldwide. Recommended by Coeliac Australia, the GESA (Gastroenterological Society of Australia), and all major international guidelines.
tTG-IgA levels correlate with the degree of intestinal damage. Very high levels (more than 10 times the upper limit of normal) are considered diagnostic even without biopsy in some paediatric guidelines. False negatives occur in IgA deficiency (approximately 2% of coeliac patients).
DGP-IgG
Detects IgG antibodies against deamidated gliadin peptides (a gluten breakdown product). Unlike tTG-IgA, this test uses the IgG class, making it useful when a patient is IgA deficient.
Role: The primary backup test when total IgA is low or deficient. Also useful in children under 2 years, where tTG-IgA may be less reliable. Some labs offer a combined tTG/DGP panel.
Older gliadin antibody tests (AGA-IgA, AGA-IgG) are now considered obsolete — they have much lower sensitivity and specificity than DGP. If your lab used the old test, request the modern DGP version.
Total IgA
Measures your total IgA antibody level. This is not a coeliac-specific test — it checks whether your body produces enough IgA antibodies in general.
Role: Should ALWAYS be ordered alongside tTG-IgA. If your total IgA is low (IgA deficiency), tTG-IgA will be falsely negative even if you have coeliac disease. IgA deficiency is 10-15 times more common in coeliac patients than the general population.
IgA deficiency affects approximately 1 in 500 Australians but approximately 1 in 40 coeliac patients. Without checking total IgA, 2-3% of coeliac cases will be missed entirely.
EMA-IgA
Detects IgA antibodies against endomysium (the connective tissue surrounding muscle fibres). Read under fluorescence microscopy by a pathologist.
Role: A confirmatory test with near-perfect specificity. Used when tTG-IgA is borderline or when there is clinical doubt. More expensive and labour-intensive than tTG-IgA because it requires manual microscopy.
Not a first-line test in Australia due to cost and complexity. Some gastroenterologists request it before proceeding to biopsy in borderline cases.
The Gluten Challenge — Why You Must Keep Eating Gluten
This is the single most important thing to know about coeliac testing: you must be eating gluten regularly for at least 6–8 weeks before your blood test. The antibodies that the blood test detects are only produced when your immune system is actively reacting to gluten. No gluten intake means no antibodies, which means a negative test — even if you have coeliac disease.
Coeliac Australia recommends consuming the equivalent of at least 2–4 slices of wheat bread per day for a minimum of 6 weeks before blood testing, and 6–12 weeks before endoscopy. Other gluten sources count too: pasta, cereals, crackers, biscuits, and anything made with wheat, rye, or barley flour.
If you have already started a gluten-free diet before being tested, discuss a formal gluten challenge with your GP. This involves reintroducing gluten for the recommended period, which can be unpleasant if you do have coeliac disease, but is necessary for accurate diagnosis. Some patients find it helps to start with small amounts and gradually increase.
False Negatives — When Tests Miss Coeliac Disease
While tTG-IgA is highly accurate, no test is perfect. Understanding why false negatives occur helps ensure you get the right diagnosis.
IgA deficiency
If your body does not produce enough IgA antibodies, the tTG-IgA test cannot detect the coeliac-specific antibodies even if they exist. This occurs in approximately 2-3% of coeliac patients.
Workaround: Always test Total IgA alongside tTG-IgA. If IgA is low, request DGP-IgG and tTG-IgG instead.
Already on a gluten-free diet
If you have been avoiding gluten for weeks or months, your antibody levels may have already dropped to normal. The blood test detects the immune reaction to gluten — no gluten, no reaction, no antibodies. This is the most common reason for a false negative.
Workaround: You MUST be eating gluten for at least 6-8 weeks before testing. This is called a gluten challenge. See section below.
Insufficient gluten intake
Even if you have not gone fully gluten-free, a very low gluten diet may reduce antibodies below the detection threshold.
Workaround: Consume the equivalent of 2-4 slices of wheat bread per day for at least 6 weeks before testing.
Young children (under 2)
IgA antibody production is still maturing in young children, making tTG-IgA less reliable. Antibody levels may fluctuate.
Workaround: Paediatric guidelines recommend tTG-IgA plus DGP-IgG in children under 2. Repeat testing may be needed.
Early coeliac disease
In the earliest stages, intestinal damage may be mild enough that antibody levels have not risen above the detection threshold yet.
Workaround: If clinical suspicion is high (family history, symptoms, associated conditions), retest in 3-6 months or proceed directly to endoscopy.
Seronegative coeliac disease
Rare but real: approximately 2-5% of biopsy-confirmed coeliac patients are persistently antibody-negative. More common in patients with lesser villous atrophy.
Workaround: If symptoms are convincing and other causes excluded, gastroscopy with duodenal biopsy may be performed regardless of serology.
After a Positive Blood Test — Biopsy Confirmation
In Australia, the standard pathway for adults is: positive blood test, then referral to gastroenterologist, then gastroscopy with duodenal biopsies, then confirmed diagnosis. The gastroscopy takes 10–15 minutes under light sedation. At least 4 biopsy samples are taken from the duodenum (the first part of the small intestine).
The pathologist grades the intestinal damage using the Marsh classification:
Marsh 0
Normal mucosa. No villous atrophy. If serology was positive, consider repeat biopsy or monitoring.
Marsh 1
Increased intraepithelial lymphocytes only. Can be caused by coeliac disease but also infections, drugs, or other conditions. Clinical context determines management.
Marsh 2
Intraepithelial lymphocytes plus crypt hyperplasia. Suggestive of coeliac disease when combined with positive serology.
Marsh 3a
Partial villous atrophy. Diagnostic of coeliac disease with positive serology.
Marsh 3b
Subtotal villous atrophy. Clear coeliac disease.
Marsh 3c
Total villous atrophy. Severe coeliac disease. The villi are completely flattened.
Who Should Be Tested for Coeliac Disease?
Coeliac Australia and GESA recommend testing for these groups. Many people with coeliac disease have no classic gut symptoms — the condition can present with anaemia, fatigue, osteoporosis, infertility, or be completely silent.
First-degree relatives of someone with coeliac disease
10-15% risk (vs 1% general population). Screening is recommended even without symptoms.
People with Type 1 diabetes
5-10% prevalence. Both are autoimmune conditions with shared genetic risk (HLA-DQ2/DQ8).
People with autoimmune thyroid disease
2-5% prevalence. Hashimoto thyroiditis is especially associated.
People with unexplained iron deficiency anaemia
Coeliac disease is the most common cause of iron deficiency in young adults that does not respond to supplements.
People with chronic diarrhoea or bloating
Classic GI symptoms, though only approximately 50% of coeliac patients have significant GI symptoms at diagnosis.
People with unexplained osteoporosis
Malabsorption of calcium and vitamin D from intestinal damage can cause bone loss, especially in premenopausal women.
People with Down syndrome or Turner syndrome
5-12% prevalence. Current guidelines recommend routine screening.
People with dermatitis herpetiformis
This itchy, blistering skin rash is the dermatological manifestation of coeliac disease. Present in approximately 15-25% of coeliac patients.
People with unexplained elevated liver enzymes
Mild ALT/AST elevation occurs in up to 40% of untreated coeliac patients and resolves on a gluten-free diet.
People with recurrent miscarriage or unexplained infertility
Untreated coeliac disease increases miscarriage risk 3-6 fold. Screening is recommended in unexplained infertility workup.
Coeliac Disease in Australia
Australia has one of the highest diagnosed rates of coeliac disease in the world. Approximately 1 in 70 Australians has coeliac disease, though 80% remain undiagnosed. The average time from symptom onset to diagnosis is 11.7 years in Australia — partly because symptoms can be subtle and partly because many GPs do not think to test.
1 in 70
Australians affected
80%
Remain undiagnosed
11.7 years
Average time to diagnosis
10-15%
Risk if first-degree relative affected
Medicare Coverage
All coeliac blood tests (tTG-IgA, Total IgA, DGP-IgG, EMA-IgA) are fully covered by Medicare when ordered by a GP. There is no out-of-pocket cost at bulk-billing pathology labs. Gastroscopy with biopsy is covered by Medicare through public hospital outpatient clinics (free) or private practice (rebate of approximately $230, with typical out-of-pocket gap of $100–$350).
After Diagnosis — What Happens Next
1. Strict gluten-free diet
Lifelong avoidance of all wheat, rye, barley, and contaminated oats. Even small amounts of gluten (as little as 50mg — a crumb of bread) can trigger the immune response and damage the intestinal lining. A dietitian consultation is essential to identify hidden gluten sources.
2. Dietitian referral
Medicare covers 5 allied health visits per year under a Chronic Disease Management plan (GP Management Plan item 721 + Team Care Arrangement item 723). Use at least one for a specialist coeliac dietitian. Coeliac Australia maintains a list of experienced dietitians.
3. Baseline nutritional screening
Blood tests for iron, folate, vitamin B12, vitamin D, calcium, and zinc. Malabsorption from intestinal damage often causes deficiencies that need supplementation during recovery. Bone density scan (DEXA) if osteoporosis risk factors are present.
4. Screen first-degree relatives
Parents, siblings, and children of diagnosed patients have a 10-15% risk. Screening is recommended even without symptoms, as silent coeliac disease still causes intestinal damage.
5. Follow-up serology
tTG-IgA is rechecked 6-12 months after starting a gluten-free diet. Antibodies should decline and normalise, confirming adherence and response. Persistent elevation suggests ongoing gluten exposure (often hidden contamination).
6. Repeat biopsy (optional)
Some gastroenterologists repeat the duodenal biopsy at 12-24 months to confirm mucosal healing. This is more common in adults where healing may be slower. Not all patients need a repeat biopsy if symptoms and serology normalise.
Frequently Asked Questions
Do I need a biopsy to confirm coeliac disease?
In most cases, yes. The current Australian standard (GESA guidelines) requires duodenal biopsy via gastroscopy to confirm the diagnosis in adults. The biopsy checks for villous atrophy — flattening of the intestinal lining caused by the autoimmune reaction. However, in children, the ESPGHAN (European) guidelines allow a no-biopsy diagnosis if tTG-IgA is more than 10 times the upper limit of normal AND EMA is positive AND the patient is symptomatic. Some Australian paediatric gastroenterologists follow this approach.
How long do I need to eat gluten before being tested?
At least 6-8 weeks of eating gluten daily (the equivalent of 2-4 slices of bread per day) is required before blood testing. For biopsy, some gastroenterologists recommend 12 weeks. This is the most important rule in coeliac testing — starting a gluten-free diet before testing can make it impossible to get a diagnosis.
Can I have coeliac disease without symptoms?
Yes. This is called silent coeliac disease and it is surprisingly common. Up to 50% of newly diagnosed coeliac patients have minimal or no classic GI symptoms. They may have been diagnosed through screening (family history, associated conditions) or incidentally through blood tests for other reasons. Even silent coeliac disease causes intestinal damage and increased risk of long-term complications.
What is the difference between coeliac disease and gluten intolerance?
Coeliac disease is an autoimmune condition with measurable antibodies, intestinal damage, and genetic markers (HLA-DQ2/DQ8). Non-coeliac gluten sensitivity (NCGS) causes symptoms similar to coeliac disease but with normal blood tests and normal biopsy. NCGS does not cause intestinal damage or long-term complications. The distinction matters because coeliac disease requires strict lifelong gluten avoidance, while NCGS may tolerate small amounts.
Is coeliac testing covered by Medicare?
Yes. tTG-IgA, Total IgA, DGP antibodies, and EMA are all covered by Medicare when ordered by a GP with a clinical indication. Gastroscopy with duodenal biopsy is also covered (either as a public hospital outpatient or private with Medicare rebate). There is no out-of-pocket cost for blood tests at bulk-billing pathology labs. Private gastroscopy typically costs $300-$600 with a Medicare rebate of approximately $230.
My tTG-IgA was slightly positive (just above the cutoff). What does that mean?
Weakly positive tTG-IgA results (just above the reference range) can occur in coeliac disease, but can also be false positives from other autoimmune conditions, liver disease, or even after a viral infection. Your GP will likely order a confirmatory EMA-IgA test or refer you directly for gastroscopy. The higher the tTG-IgA level, the more likely the result is a true positive.
Related Reading
Track Your Coeliac Markers Over Time
Upload your blood test results and see your tTG antibody levels, iron studies, and nutritional markers tracked over time — showing how your body is responding to a gluten-free diet.
This information is based on guidelines from the Gastroenterological Society of Australia (GESA), Coeliac Australia, and the Royal College of Pathologists of Australasia (RCPA). Reference ranges may vary between pathology providers. SmarterBlood provides educational information only and is not a substitute for professional medical advice.