Is There a Test for ME/CFS?

Why Is There No Single Test for ME/CFS?

The CDC says: "There is no confirmatory test currently available to diagnose ME/CFS." It adds that people with ME/CFS "often are found to have biological abnormalities," yet none of these biomarkers has "sufficient sensitivity and specificity to constitute a diagnostic test" (CDC). Healthcare providers diagnose it instead from "a thorough medical history and physical exam, laboratory test results, and ruling out other fatiguing illnesses with a targeted work-up."

NICE's 2021 ME/CFS guideline tells clinicians to explain to patients "that there currently is no diagnostic test for ME/CFS and it is recognised on clinical grounds alone" (NICE, 2021). Our article on diagnosing chronic fatigue syndrome follows 3 patients with the same diagnosis and different causes.

What Do Routine Blood Tests Check For?

When ME/CFS is suspected, NICE lists investigations "to exclude other diagnoses" (NICE, 2021):

• urinalysis for protein, blood and glucose
• full blood count
• urea and electrolytes
• liver function
• thyroid function
• erythrocyte sedimentation rate or plasma viscosity
• C-reactive protein

NICE leaves further tests to clinical judgement, for example vitamin D, vitamin B12 and folate levels, serological tests if there's a history of infection, and a 9am cortisol for adrenal insufficiency.

Why Do Symptoms Count More Than Test Results?

Without a confirmatory test, the diagnosis rests on a pattern of symptoms. The CDC lists the core features: an assessment begins when a patient presents with "impaired function accompanied by fatigue, post-exertional malaise (PEM), unrefreshing sleep, and either one or both cognitive impairment or orthostatic intolerance" (CDC). The Institute of Medicine (now the National Academy of Medicine) defines PEM as "an exacerbation of some or all of an individual's ME/CFS symptoms after physical or cognitive exertion, or orthostatic stress that leads to a reduction in functional ability." The IOM also found that cognitive impairment and orthostatic intolerance "have distinctive findings in these individuals that, particularly when viewed together with the core symptoms, distinguish ME/CFS from other fatiguing disorders" (Institute of Medicine, 2015). NICE and the CDC set different minimum symptom lengths, which our guide to what kind of doctor treats ME/CFS compares.

Used today Research only

Replay

Where Does Upright and Autonomic Testing Fit?

NICE tells clinicians to "be aware that people with ME/CFS may experience orthostatic intolerance, including postural orthostatic tachycardia syndrome (POTS)." Its glossary describes orthostatic intolerance as symptoms such as light-headedness, near-fainting or fainting, impaired concentration, headaches and dimming or blurring of vision that "occur or worsen on standing up." NICE says to refer people with orthostatic intolerance to secondary care if their symptoms are severe or worsening, or if another condition may be the cause (NICE, 2021).

Some research teams also measure blood flow to the brain during upright testing. Our guide to autonomic testing covers tilt studies that measure brain blood flow in ME/CFS. A 2025 systematic review describes ME/CFS as a condition in which "a large proportion of patients" experience orthostatic intolerance, and it found significantly reduced brain blood flow in 12 of the 26 studies of ME/CFS alone, while noting that orthostatic intolerance "may be a confounding factor" in many of them (Christopoulos, 2025). These are research findings. Neither the CDC nor the NICE criteria quoted above list them as diagnostic tests.

In our team's video on orthostatic intolerance, the team explains why it doesn't rely on heart rate alone: blood pressure in the body can look normal while the pressure driving blood into the brain changes on standing. The video lists chronic fatigue syndrome among the conditions it applies to.

What About the ME/CFS Blood Test in the News?

In 2019, researchers published a nanoelectronics blood assay for ME/CFS in the Proceedings of the National Academy of Sciences (Esfandyarpour, 2019). The NIH's summary says the test, "in a pilot study, accurately identified people with myalgic encephalomyelitis/chronic fatigue syndrome," and that "more studies are needed to confirm these findings and ensure the assay is specific for ME/CFS before it could be used in the clinic" (NIH).

In 2025, another research group reported a blood test based on chromosome conformation markers, from a retrospective study of 47 people with severe ME/CFS and 61 healthy controls (Hunter, 2025). Like the 2019 pilot, it's a research result: the authors describe its "first testing" in a retrospective validation group, not use in the clinic.

Can an Exercise Test Show PEM?

Studies of a 2-day exercise test disagree on whether it can. Testing with 2 cardiopulmonary exercise tests (CPETs) done 24 hours apart is "increasingly used to determine post-exertional malaise (PEM) and disability" in ME/CFS, according to the authors of a 2026 study, who note that earlier reports were inconsistent (Mancini, 2026). That study ran a maximal bicycle test on 2 consecutive days in 58 people with ME/CFS and 25 control subjects. Peak oxygen uptake and the other main gas-exchange measures didn't fall on day 2 in either group, and the authors concluded: "The data do not support using the 2-day CPET protocol to define PEM or disability."

An earlier study of 22 people with ME/CFS reported the opposite: peak oxygen uptake and other measures fell on the second test, and its authors concluded that repeated CPETs "warrant consideration as a clinical indicator for diagnosing ME/CFS" (Keller, 2014). The 2 sets of results disagree, so the question isn't settled.

Testing for ME/CFS: FAQ