How ME/CFS is diagnosed

Getting an ME/CFS diagnosis takes time. There is no single blood test or scan that confirms it. The process can take months or even years.

IIn the past, ME/CFS was diagnosed largely by ruling out other conditions. If nothing else explained the symptoms, doctors assumed it was ME/CFS.

Current guidance takes a more active approach. Doctors now look for a specific symptom pattern, particularly PEM.

In England and Wales, ME/CFS is diagnosed using NICE guideline NG206, the national guidance the NHS follows. Under it, ME/CFS is suspected when all four of the symptoms below are present.

Two further conditions apply. Your ability to manage work, education, social life, or personal activities must be significantly reduced compared with before you became ill. The symptoms must also not be explained by another condition.

1. Debilitating fatigue. Worsened by activity, not caused by excessive exertion, and not significantly relieved by rest.
2. Post-exertional malaise. Symptoms worsen after activity. The worsening is often delayed by hours or days, is out of proportion to what caused it, and can take hours, days, weeks, or longer to settle.
3. Unrefreshing sleep, disturbed sleep, or both. Waking exhausted or flu-like, broken or shallow sleep, an altered sleep pattern, or sleeping far more than usual.
4. Cognitive difficulties. Often called brain fog. Problems finding words or numbers, slowed responses, short-term memory difficulties, and trouble concentrating or multitasking.

All four are needed. A doctor can suspect ME/CFS once these have persisted for six weeks in adults, or four weeks in children and young people. The diagnosis is confirmed after three months.

A note on the six month figure

You may see six months quoted elsewhere. That figure comes from the 2015 US criteria, which are still in use internationally. In England and Wales, the three-month threshold has applied since 2021.

The guidance does not treat diagnosis as the end of the process. Adults should be referred directly to an ME/CFS specialist team to confirm the diagnosis and agree a care and support plan.

Children and young people should be referred to a paediatrician for assessment, and then to a paediatric ME/CFS specialist team.

In practice, access to specialist teams varies considerably across the UK, and waits can be long. The referral is still worth asking for. Where ME/CFS is managed in primary care, the guidance expects that care to be supported by advice and direct clinical consultation from a specialist team.

There is no single test that diagnoses ME/CFS. Tests are used to rule out other conditions with overlapping symptoms.

Standard blood work

The guidance sets out a standard panel: full blood count, urea and electrolytes, liver function, thyroid function, inflammatory markers (ESR or plasma viscosity, and CRP), calcium and phosphate, HbA1c, serum ferritin, coeliac screening, creatine kinase, and a urine test.

Depending on your history, a doctor may add others, such as vitamin D, vitamin B12 and folate, a morning cortisol test, or tests for a specific past infection.

In ME/CFS these results usually come back normal. That can be disheartening, but normal results are what the guidance expects. They are ruling other conditions out, not testing for ME/CFS.

Specialised tests

These are not routine, but may be arranged depending on your symptoms.

A tilt table test assesses orthostatic intolerance and can identify POTS. A sleep study rules out sleep apnoea as a cause of unrefreshing sleep. A neurology assessment checks for nerve-related conditions that could explain symptoms.

Brain fog makes it harder to think clearly during appointments. A little preparation helps.

Keep a symptom log. Write down which activities trigger your symptoms, and roughly how long it takes for the crash to follow.

Bring someone with you. A trusted person can take notes and help explain your experience to the doctor.

Narrow it down to three. Doctors often have limited time. Write down your three most significant symptoms before you go and focus on those.

A diagnosis gives a clearer starting point for understanding and managing the illness.

You do not have to wait for one to start protecting yourself. If activity reliably triggers a delayed worsening of symptoms, it is safer to assume the pattern applies to you. Pace accordingly until you have clearer information. See the pacing guide.