Coeliac Disease: Why Most People With It Don't Know They Have It

A Common Condition Hiding in Plain Sight

Coeliac disease affects approximately 1 in 100 people in the UK [1], yet according to Coeliac UK, only around 36% of cases are currently diagnosed [2]. That means roughly 500,000 people are living with a condition that is gradually damaging their small intestine, without ever knowing it.

Unlike a food intolerance, coeliac disease is a serious autoimmune condition. When someone with coeliac disease eats gluten (found in wheat, barley, and rye), their immune system attacks the lining of the small intestine, causing inflammation and a process called villous atrophy, where the tiny finger-like projections that absorb nutrients are progressively flattened. Over time, this impairs the absorption of iron, calcium, folate, and other essential nutrients.

Why So Many Cases Go Undiagnosed

The classic textbook picture of coeliac disease involves chronic diarrhoea, bloating, and weight loss. But many people present with far subtler signs that are easily attributed to other conditions. Common but frequently overlooked symptoms include:

• Persistent fatigue and low energy

• Iron deficiency anaemia that doesn't respond to oral supplements

• Recurrent mouth ulcers

• Joint pain or bone thinning (osteoporosis)

• Brain fog and difficulty concentrating

• Unexplained skin rashes, particularly a blistering rash known as dermatitis herpetiformis

• Recurrent miscarriage or unexplained fertility problems

Because these symptoms overlap with many other conditions, coeliac disease is frequently missed. According to Coeliac UK, the average time from symptom onset to diagnosis is 13 years [2]. NICE guideline NG20 specifically recommends that coeliac disease should be considered in patients presenting with chronic fatigue, anaemia, and unexplained gastrointestinal complaints [3], and that it should be excluded before a diagnosis of IBS is made. In practice, this step is often skipped.

What the Blood Test Measures

The first-line screening test for coeliac disease is a blood test measuring tissue transglutaminase IgA antibodies (tTG-IgA). A systematic review by Sheppard et al. (2022), pooling 113 studies and over 28,000 participants, found that tTG-IgA testing has a sensitivity of over 90% in adults and over 97% in children [4]. This makes it one of the most reliable screening tools in medicine, though it's important to understand two key limitations.

First, a positive tTG-IgA result is not a diagnosis on its own. NICE NG20 requires that adults with positive serology are referred to a gastroenterologist for an endoscopic intestinal biopsy, which remains the gold standard for confirming villous atrophy and formalising the diagnosis [3]. You should not start a gluten-free diet based on a blood test alone, as this can make the confirmatory biopsy unreliable.

Second, approximately 2% of people with coeliac disease have selective IgA deficiency, meaning their immune system produces very little IgA antibody [5]. In these patients, the standard tTG-IgA test will return a false negative, even if active coeliac disease is present. If your total IgA level is low and your symptoms persist, your GP can request an alternative IgG-based test (such as deamidated gliadin peptide IgG) to investigate further.

The Gluten Challenge: Getting the Timing Right

For the tTG-IgA test to be accurate, you must be eating gluten regularly before testing. NICE NG20 is specific about this: you should eat gluten in more than one meal every day, for at least six weeks before the blood test [3]. Eating less gluten than this risks insufficient antibody production and a false-negative result.

If you've already cut gluten from your diet and want to be tested, you'll need to reintroduce it for the full six-week period. This can be uncomfortable if you do have coeliac disease, but it's essential for a reliable result.

Why Early Detection Matters

A comprehensive review by Lebwohl et al. in The Lancet (2018) found that untreated coeliac disease is associated with increased risk of osteoporosis, fertility complications, and certain intestinal lymphomas [5]. The mechanisms are well understood: chronic villous atrophy causes malabsorption that depletes calcium (affecting bone density), iron (causing anaemia), and folate (affecting fertility and neurological health).

A strict gluten-free diet, when started early enough, can reverse intestinal damage and significantly reduce these long-term risks. That's why screening matters, particularly for people who have been living with unexplained symptoms for years.

Who Should Consider Testing?

Clinical guidelines suggest testing is appropriate for individuals who:

• Experience persistent bloating, abdominal discomfort, or altered bowel habit

• Have unexplained iron, folate, or vitamin B12 deficiency

• Suffer from chronic fatigue not explained by other causes

• Have a first-degree relative with coeliac disease (this increases your risk to approximately 1 in 10)

• Have another autoimmune condition such as type 1 diabetes or autoimmune thyroid disease

• Have been given a diagnosis of IBS without coeliac screening

When to See Your GP

A private blood test can be a useful starting point, but you should see your GP urgently if you experience:

• Severe, unintended weight loss

• Persistent gastrointestinal bleeding (blood in stools, or dark/black stools)

• Refractory anaemia that isn't responding to treatment

• Symptoms in a child, including failure to thrive, persistent diarrhoea, or poor growth

If your Brooksby results show elevated tTG-IgA antibodies, take your report to your GP. The next step is a referral to gastroenterology for a confirmatory endoscopic biopsy. Do not start a gluten-free diet before this biopsy is completed, as removing gluten can cause the intestinal lining to heal and make the biopsy unreliable.

How Brooksby Medical Can Help

The Brooksby Medical Coeliac Disease Antibody Blood Test (£89) measures tTG-IgA antibodies, the first-line screening marker recommended by NICE. It's a simple finger-prick blood test you can do at home, with results reviewed and reported by a practising GP within two to three working days.

If you're also experiencing lower bowel symptoms such as a change in bowel habit, blood in your stools, or abdominal pain, a private qFIT test can help investigate those alongside coeliac screening.

References

1. West J, et al. Incidence and prevalence of celiac disease and dermatitis herpetiformis in the UK over two decades. Am J Gastroenterol. 2014;109(5):757-768

2. Coeliac UK. Getting diagnosed: the key facts. 2024. coeliac.org.uk

3. NICE. Coeliac disease: recognition, assessment and management (NG20). 2015 (updated 2024). NICE.org.uk

4. Sheppard AL, et al. Systematic review with meta-analysis: the accuracy of serological tests to support the diagnosis of coeliac disease. Aliment Pharmacol Ther. 2022;55(5):514-527

5. Lebwohl B, et al. Coeliac disease. The Lancet. 2018;391(10115):70-81

Written by Dr James Coleman, GP and founder of Brooksby Medical. Dr Coleman is a practising General Practitioner who founded Brooksby Medical to give patients direct access to the blood tests and clinical interpretation they need, without waiting lists.

Medically reviewed: March 2026 | Next review due: March 2027

Medical disclaimer: This article is for informational purposes only and does not constitute medical advice. Blood test results should always be interpreted by a qualified healthcare professional in the context of your individual symptoms, medical history, and clinical picture. If you have concerns about your health, please consult your GP.