There are around 20,000 people in Wales living with an undiagnosed autoimmune disease.
The startling figure, concerning Coeliac disease, has been highlighted by charity Coeliac UK as part of this May's Coeliac Awareness Month campaign.
The initiative aims to encourage individuals and parents to recognise symptoms of the disease and to undertake a simple blood test.
This can help prevent possible future health complications such as osteoporosis, recurrent miscarriage, small bowel cancer, and intestinal lymphoma.
Coeliac disease is currently affecting 1 in 100 people, but only 36 per cent of those affected in Wales are diagnosed.
The consequence of eating gluten — a protein found in wheat, barley and rye — for people with the condition, is an autoimmune response that attacks the body's own tissues, potentially causing serious gut damage and other health issues.
A case study highlighted by the charity involves Trudy, 54, from Wales.
She had endured unexplained pain and discomfort for years, saying: "When I used to wake up at night with a painful tummy, I now realise that it could have been a high gluten day."
She was only diagnosed after a referral to a GP specialising in the disease.
"When I was diagnosed, I contacted Coeliac UK who put me in touch with a mentor who was lovely and helped me with advice," Trudy shared on her journey to recovery.
Coeliac UK has an online self-assessment based on NICE guidelines.
This provides recommendations to speak with a healthcare professional about the possibility of getting tested.
Nonetheless, Coeliac UK CEO, Hilary Croft highlighted the importance of not prematurely removing gluten from diets.
She stated: "It is so important that we raise awareness of coeliac disease so we can improve diagnosis and get those with undiagnosed coeliac disease on the road to recovery."
For further advice and information on Coeliac Awareness Month, visit the Coeliac UK website.
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