Recognise the symptoms
Celiac disease presents differently in different people. Classic symptoms include chronic diarrhoea, bloating, abdominal pain, and weight loss. However, many people experience atypical symptoms — fatigue, anaemia, joint pain, skin rashes (dermatitis herpetiformis), mouth ulcers, or neurological symptoms like brain fog and peripheral neuropathy. Some people are entirely asymptomatic. If you or a family member has any combination of these symptoms, especially with a first-degree relative diagnosed with celiac, speak to a GP about testing.
Do NOT go gluten-free before testing
This is the most common mistake people make. If you stop eating gluten before your blood tests or biopsy, the results will be falsely negative. The immune markers and intestinal damage that doctors look for require active gluten consumption to be detectable. Continue eating gluten normally — ideally 1–2 slices of bread per day — until all testing is complete.
Blood tests — the first line of investigation
Your doctor will order a serology panel. The primary test is anti-tissue transglutaminase IgA (tTG-IgA), which detects antibodies the immune system produces when attacking the gut lining. A total serum IgA is also measured to rule out IgA deficiency, which affects about 2–3% of celiac patients and would cause a false negative on the tTG-IgA test. Additional antibodies that may be tested include anti-endomysial antibody (EMA) and deamidated gliadin peptide antibodies (DGP-IgA and DGP-IgG).
Elevated antibodies → referral for biopsy
A positive or elevated blood test is strong evidence of celiac disease, but confirmation requires a small intestinal biopsy. You will be referred to a gastroenterologist for an upper endoscopy (gastroscopy). During this procedure, small tissue samples (biopsies) are taken from the duodenum — the first section of the small intestine. This is usually done under mild sedation and takes about 15–20 minutes.
Biopsy — what doctors look for
The biopsy samples are examined under a microscope. Pathologists use the Marsh Classification to grade the degree of damage:
• Marsh 0: Normal — no damage • Marsh 1: Increased intraepithelial lymphocytes (early changes) • Marsh 2: Crypt hyperplasia (deeper changes) • Marsh 3a/b/c: Partial to total villous atrophy (definitive celiac) • Marsh 4: Hypoplastic atrophy (rare, severe)
A diagnosis of celiac disease is confirmed when Marsh 2 or higher changes are found alongside positive serology.
Genetic testing (HLA typing)
HLA-DQ2 and HLA-DQ8 gene testing is not used to diagnose celiac disease — it is used to rule it out. Almost all people with celiac carry these variants. If someone tests negative for both, celiac disease is extremely unlikely. This test is particularly useful for people who are already gluten-free and cannot complete a gluten challenge, or for clarifying ambiguous biopsy results.
Starting the gluten-free diet
Once a confirmed diagnosis is made, a strict, lifelong gluten-free diet begins immediately. You will typically be referred to a dietitian who specialises in celiac disease. They will help you understand which foods and ingredients to avoid, how to prevent cross-contamination, and how to ensure nutritional adequacy. Follow-up blood tests at 6 and 12 months are standard to confirm that tTG-IgA levels are falling, indicating intestinal healing.
Monitoring and follow-up
Celiac disease requires lifelong monitoring. Annual or biannual blood tests, bone density scans (due to malabsorption of calcium and Vitamin D), and checks for associated conditions (thyroid disease, Type 1 diabetes) are recommended. First-degree relatives — parents, siblings, and children — should be tested even if they have no symptoms, as the condition is strongly hereditary.