Scientists in the United Kingdom say they have developed a blood test that can diagnose myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) with 96% accuracy – the first of its kind.

For many who live with the debilitating condition, this will be exciting news.

Despite affecting millions of people worldwide, this condition remains poorly understood. It is characterised by unrelenting fatigue that doesn’t improve with rest, and post-exertional malaise – a worsening of symptoms after even minor physical or mental activity.

Yet with no reliable test, many people wait years for a diagnosis. This usually depends on symptoms meeting certain clinical criteria. But diagnostic criteria can be controversial as they vary worldwide and many are outdated.

An accurate blood test could be a game changer for diagnosis.

So, how excited should we get? Here’s what we know.

How diagnosis works without a test

Currently, you can only receive a diagnosis if you experience disabling fatigue – one of the key symptoms according to most clinical criteria – for at least six months, accompanied by post-exertional malaise.

But people with the condition often experience a wide range of other symptoms, including headaches, muscle or joint pain, sleep disturbances, dizziness, a racing heart, and problems with memory, thinking and decision making.

So, clinicians must also rule out other conditions with overlapping symptoms.

This means diagnosis relies heavily on clinicians’ knowledge of ME/CFS and their willingness to listen to the patient’s complex symptom history. This process can take years – and the delay in diagnosis has real consequences.

Evidence suggests early intervention is key to recovery. Rest during the early stages of the illness likely results in better long-term outcomes, as has been suggested for the clinically similar disease long COVID.

One study showed a delayed ME/CFS diagnosis was linked to poorer outcomes, meaning recovery was less likely and the chance of developing more severe symptoms increased.

Without a definitive diagnosis, patients regularly face disbelief about their illness and have limited access to information, health-care services and medical benefits.

Frequent delays in diagnosis may contribute to the condition’s low recovery rate, which is estimated at just 1–10%.

What the new study looked at

To develop a diagnostic test, the new study identified biomarkers that may be specific to people with this condition.

In this case, the biomarkers relate to epigenetics – changes in the structure of a person’s chromosomes, influencing which genes can be turned on or off.

These changes occur due to environmental influences such as stress, infection and exercise. So, when someone develops ME/CFS, the illness may change the structure of their chromosomes – but until now researchers hadn’t identified what this would look like.

The researchers examined blood samples from people they knew had ME/CFS and identified around 200 such biomarkers. These changes formed a distinct biological “signature” that was not present in the blood of healthy participants in the comparison group.

This signature was very accurate in correctly identifying which samples were from people with the condition and which were from the comparison group.

According to the researchers, the test’s sensitivity was 92% – this is the probability a positive result will show when someone has the condition. It had a specificity of 98%, meaning the probability it can rule out negative cases.

This combined to an overall diagnostic accuracy of 96%.

So, is this a breakthrough?

This research is promising, but it’s still very early days. It was a proof-of-concept study, meaning small-scale research to initially test whether an idea might work.

In this case, researchers explored the idea that structural changes in chromosomes could be used as biomarkers of ME/CFS. Their results suggest they can.

However, there were several limitations. The study involved a relatively small number of people: 47 participants with severe ME/CFS and 61 in the healthy “control” group.

The ME/CFS group had more females, and its participants were so severely affected they were housebound. So they presumably had lower activity levels than the control group.

We know a person’s sex and activity levels can influence these chromosomal changes, so this may have affected the results.

To develop a diagnostic test that can be used widely, several crucial steps remain.

How much a person’s sex and exercise levels influence these biomarkers needs to be determined. The biomarkers will also need to be validated in larger, more diverse groups, which include people with less and more severe symptoms than in this study and those from different backgrounds.

To confirm these biomarkers are truly specific to ME/CFS, they need to be compared with other conditions that share similar symptoms, such as multiple sclerosis and fibromyalgia.

Finally, it’s also important that a test, if developed, should be affordable and accessible.

ME/CFS remains a severely underdiagnosed condition, and the lack of a reliable test continues to delay care and worsen outcomes. Identifying biomarkers, as this study aimed to do, is a promising first step.

Sarah Annesley, Senior Postdoctoral Research Fellow in Cell and Molecular Biology, La Trobe University

This article is republished from The Conversation under a Creative Commons license. Read the original article.