GI Investigations · Patient Guide
Coeliac Testing: Blood Test First, Biopsy to Confirm
A two-step diagnosis with one absolute rule: the tests only work if you're still eating gluten.
Coeliac disease — an autoimmune reaction to gluten that damages the small bowel lining — affects roughly 1 in 100 people, most undiagnosed. Its symptoms are famously nonspecific: bloating, fatigue, loose stools, iron deficiency. Testing is straightforward and accurate, with one rule that overrides everything: both the blood test and the biopsy require you to be eating gluten when tested. Going gluten-free first sabotages the diagnosis.
How the two-step diagnosis works
Step one is a blood test for tTG antibodies (with total IgA measured alongside, since IgA deficiency can mask the result). Step two, for positive or equivocal results, is confirmation by duodenal biopsies taken during a short gastroscopy — still the adult standard, and easily combined with the endoscopy many of these patients need anyway for anaemia or symptoms.
When this test is usually indicated
- Persistent bloating, loose stools or IBS-type symptoms — coeliac screening is part of the standard work-up
- Unexplained iron-deficiency anaemia or low B12/folate
- Unexplained fatigue with gut symptoms, or unexplained weight loss
- First-degree relatives of confirmed coeliac patients
- Type 1 diabetes and autoimmune thyroid disease, which cluster with coeliac
When it may not be the right test
- Testing after weeks on a gluten-free diet — antibodies and bowel healing produce false negatives; a gluten challenge is needed first
- Home food-intolerance tests as a substitute — IgG food panels do not diagnose coeliac disease
- Repeating antibody tests indefinitely for monitoring instead of clinical review
- Genetic (HLA) testing as a routine first step — its role is specific and limited
If you've already gone gluten-free and feel better, the honest options are a supervised gluten challenge before testing, or accepting an unconfirmed diagnosis — with the downsides that brings for prescriptions, follow-up and family screening. Testing before the diet starts avoids the dilemma entirely.
What happens if you do need it
A positive blood test leads to gastroscopy with duodenal biopsies — a few extra seconds within a test that takes minutes, performed by Mr Papettas as a JAG-accredited endoscopist. Confirmed coeliac disease is then managed with dietitian support and appropriate follow-up; the gluten-free diet, started after confirmation, is the treatment.
Frequently asked questions
How much gluten do I need to eat before testing?
Guidance is gluten in more than one meal daily for at least six weeks before testing — a genuine gluten challenge, not a token biscuit.
Is the blood test reliable?
tTG serology is excellent when done on a gluten-containing diet with IgA levels checked — that's why it's the universal first step.
Why is a biopsy still needed?
In adults, biopsy confirmation remains the standard — it secures a lifelong diagnosis and baseline before committing to a permanent diet.
Can coeliac disease appear later in life?
Yes — it can present at any age, which is why new symptoms in adulthood still warrant screening.
What happens if coeliac is confirmed?
A strict gluten-free diet with dietitian support, correction of deficiencies, and family screening advice — the bowel lining typically recovers on the diet.
How do I get tested privately?
Bloods at consultation and, if positive, gastroscopy within days — call 01926 935121.
Related reading
Unsure whether you need this test?
Mr Trif Papettas FRCS is a Consultant Colorectal and General Surgeon at Nuffield Health Warwickshire Hospital, Leamington Spa, and a JAG dual-accredited endoscopist. A consultation settles which investigation, if any, your symptoms actually need — and if a test is indicated, it can usually be arranged within days.
Self-referrals welcome · No GP letter required · Self-pay and insured patients seen at Nuffield Health Warwickshire Hospital, Leamington Spa CV32 6RW