Biopsy

Blood tests can suggest coeliac disease. A biopsy confirms it. If you’ve been told you have coeliac disease based on a blood test alone, or that you probably have it without ever having a biopsy, it’s worth understanding what that means — and whether your diagnosis is complete.

What Is a Biopsy in Coeliac Diagnosis?

A duodenal biopsy is the gold-standard diagnostic test for coeliac disease. During an upper endoscopy (gastroscopy), a specialist takes small tissue samples — usually four to six — from the lining of the small intestine, specifically the duodenum. These samples are examined under a microscope for signs of villous atrophy: the flattening and damage of the tiny finger-like projections (villi) that line the gut and absorb nutrients.

The degree of damage is graded using the Marsh classification, from Marsh 1 (increased inflammatory cells, villi still intact) to Marsh 3 (complete villous atrophy). A Marsh 3 finding, combined with a positive TTG-IgA blood test and improvement on a gluten-free diet, gives a confident coeliac diagnosis.

One critical rule: you must be eating gluten regularly before the biopsy. If you’ve already cut out gluten, the gut may have started healing and the biopsy can return a false negative. Going back on gluten for 6–8 weeks before testing — a gluten challenge — is standard practice. It’s unpleasant. But an incomplete test means an incomplete diagnosis.

In children, some guidelines (including ESPGHAN) allow diagnosis without biopsy if TTG-IgA levels are extremely elevated and other markers align. But for adults, the biopsy remains the standard.

Follow-up biopsies are also used to assess whether the gut has healed after going gluten-free — typically 12–24 months after diagnosis. Healing confirms you’ve eliminated gluten effectively. Persistent damage prompts investigation into hidden gluten sources or other conditions.

What This Means for You

If you haven’t had a biopsy, push for one before committing to a lifelong gluten-free diet. A diagnosis built only on symptoms or a single blood test leaves too many questions open. And if you’ve been gluten-free for a while and a biopsy is now being suggested, ask your doctor about a supervised gluten challenge first — so the test actually tells you something meaningful.

Related in the Coeliac Alphabet: TTG / Tissue Transglutaminase · Villous Atrophy · Diagnosis FAQ · back to the full A–Z.