A new blood test can diagnose chronic fatigue syndrome, also known as CFS or ME, with an accuracy of 96%, according to scientists who developed it.
The researchers, from the University of East Anglia, hope the breakthrough could pave the way for a similar test to diagnose long COVID.
But other scientists warn the test needs to be independently validated in further clinical studies before being offered privately to patients who may be desperate to understand their debilitating symptoms.
CFS is a disabling illness characterised by extreme fatigue that is not relieved by rest.
Around 400,000 people in the UK have the condition, but its cause and treatment has been controversial.
Professor Dmitry Pshezhetskiy, lead researcher, said: “We know that some patients report being ignored or even told that their illness is ‘all in their head’.
“With no definitive tests, many patients have gone undiagnosed or misdiagnosed for years.
“Our discovery offers the potential for a simple, accurate blood test to help confirm a diagnosis, which could lead to earlier support and more effective management.”
The researchers used technology developed by biotech company Oxford BioDynamics to analyse how DNA is folded in blood samples taken from 47 patients with severe symptoms and 61 people who were healthy.
Each of our cells contain about two metres of DNA, which is tightly packed and folded millions of times. The folds aren’t random – they help turn genes on or off.
The folding and 3D structure of the genetic material isn’t determined by the DNA code which we are born with and is largely fixed.
Instead, life events can influence the folding, and which genes are active, a mechanism called “epigenetics”.
The researchers found people with CFS had a unique pattern in epigenetic markers, or chemical tags, on their DNA.
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A test based on the pattern was able to identify 92% of people with CFS and 98% of those who were healthy. The overall accuracy was 96%.
“This is a significant step forward,” said Prof Pshezhetskiy.
“For the first time, we have a simple blood test that can reliably identify ME/CFS – potentially transforming how we diagnose and manage this complex disease.
“Post-COVID syndrome, commonly referred to as long COVID, is one example of ME/CFS, where a similar cluster of symptoms is triggered by the COVID-19 virus, rather than by other known causes such as glandular fever.
“We therefore hope that our research will also help pave the way for a similar test to accurately diagnose long COVID.”
The study has been published in the Journal of Translational Medicine.
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Prof Chris Ponting, from the University of Edinburgh, who wasn’t involved in the research, said the claims were premature because there were significant differences in sex, age and other factors between the people with CFS and the healthy controls.
“This test needs to be fully validated in better designed and independent studies before it is considered for clinical application,” he said.
“Even if validated, the test will be expensive, likely around £1,000.”
