ME/CFS test: how ME/CFS is diagnosed, and what blood tests can and cannot show

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a serious, long-term illness that the CDC describes as biological (CDC). In 2021 and 2022, 1.3% of US adults had ME/CFS, with women affected more than men (CDC, NCHS Data Brief 488).

No laboratory test confirms it. Clinicians use the 2015 criteria, which require three core symptoms: a substantial drop in activity with fatigue lasting more than six months; post-exertional malaise, a worsening of symptoms after exertion that the person would have tolerated before the illness; and unrefreshing sleep. At least one of two further features must be present: cognitive impairment, or orthostatic intolerance, a worsening of symptoms when upright (CDC; CDC symptoms page).

ME/CFS can be part of long COVID: the 2024 National Academies definition names it among the conditions long COVID can include (NASEM, 2024). Our article on whether there is a test for ME/CFS covers the question in more detail.

Research has not confirmed a single mechanism. A 2023 systematic review of candidate biomarkers found no validated one and little agreement between studies, while several studies supported immune involvement in the illness (BMC Medicine, 2023). Our piece on ME/CFS and the immune system walks through that research.

Immune signalling offers one frame for the symptoms. Cytokines released during infection act on the brain and produce the fatigue, malaise, disturbed sleep and poor concentration of sickness behaviour, and a 2008 review describes how that signalling can deepen when immune activation continues (Dantzer et al., 2008). The frame fits several ME/CFS symptoms, and it remains one hypothesis among several.

Post-exertional malaise is central to the 2015 criteria (CDC). The CDC describes it as a worsening of symptoms after even minor physical or mental exertion (CDC). The guide to fatigue and post-exertional malaise explains how it differs from other kinds of fatigue. Cognitive impairment, which people with ME/CFS call brain fog (CDC), is one of the two further features in the criteria, and the brain fog guide covers it.

Blood tests in an ME/CFS evaluation look for other explanations. The CDC's guidance for clinicians lists basic screening tests: a complete blood count with differential, electrolytes, glucose, kidney and liver tests, calcium, phosphorus and magnesium, thyroid tests, ESR, CRP, antinuclear antibodies, rheumatoid factor and urinalysis (CDC). A diagnosis of ME/CFS rests on the symptom criteria after clinicians have excluded other conditions (BMC Medicine, 2023).

That makes normal results part of the path to diagnosis. They leave most immune signalling unmeasured: CRP reads inflammation downstream of IL-6 (Hunter and Jones, 2015), and a standard panel includes no interferons, chemokines or T-cell markers. Online questionnaires can match symptoms to the criteria and confirm nothing; our guide to online chronic fatigue syndrome tests versus blood tests compares the two.

An evaluation for ME/CFS runs on your history, so the record you bring shapes it. Four things help:

• A timeline. The date the illness began, what came before it (an infection, for example), and how your activity level has changed since.
• A post-exertional malaise log. Your activities each day and how you felt that day and the two after it. The pattern of effort followed by a later crash is what the criteria ask about.
• Sleep and standing. Your sleep quality, and any worsening of symptoms when you stand or sit upright for a while.
• Previous results. Copies of earlier blood tests, so your doctor can see what earlier tests covered and when.

This record helps whichever tests your doctor chooses, and it gives any later measurement a baseline to set it against.

A broad panel measures the immune proteins a screening workup leaves out: cytokines such as IL-6 and TNF-α, interferons such as IFN-γ, chemokines such as IP-10, and T-cell markers such as PD-1, LAG-3 and Granzyme B. The panel places each against a healthy reference, and a retest shows which way each moves. For a fluctuating illness, a series of results read beside a symptom and activity diary gives you and your doctor objective data across good and bad periods.

The limits follow from the research. Research has validated no biomarker for ME/CFS, so no panel can diagnose it, and group differences in studies do not translate into a verdict about one person (BMC Medicine, 2023). A panel cannot choose a treatment.

Mune Mirror™^* is currently in development, and the performance characteristics of this test have not yet been established. It is investigational. It does not diagnose, detect, screen for, treat, cure or prevent any disease. Results are for research and informational purposes, to discuss with your own doctor.

The guide to unwellness testing explains how this measurement fits beside standard care.

Mune Mirror™ measures more than 1,000 immune and inflammation proteins from an at-home sample, including T-cell and interferon markers, and benchmarks each against a healthy reference. Repeated over time, it gives you a measured record across the ups and downs of ME/CFS to bring to your doctor. It does not diagnose ME/CFS.

Is there a blood test for ME/CFS?

No. A 2023 systematic review found no validated diagnostic biomarker for ME/CFS. Blood tests in an evaluation look for other conditions that could explain the symptoms, and clinicians diagnose ME/CFS from the 2015 criteria.

How is chronic fatigue syndrome diagnosed?

Clinicians use the 2015 criteria: a substantial drop in activity with fatigue for more than six months, post-exertional malaise and unrefreshing sleep, plus cognitive impairment or orthostatic intolerance. Screening tests look for other explanations first.

What is post-exertional malaise in ME/CFS?

The CDC describes post-exertional malaise as a worsening of symptoms after even minor physical or mental exertion that the person would have tolerated before. It is one of the three core symptoms the 2015 criteria require.

Can long COVID include ME/CFS?

Yes. The 2024 National Academies definition of long COVID names ME/CFS among the conditions long COVID can include. The same 2015 criteria apply.

How common is ME/CFS?

In 2021 and 2022, 1.3% of US adults had ME/CFS, according to the CDC's National Center for Health Statistics, and women had it more than men.

Why do my blood tests come back normal with ME/CFS?

Standard tests look for other conditions, and ME/CFS has no validated diagnostic biomarker, so normal results are expected and form part of the path to diagnosis. They say little about immune signalling, which a standard panel does not measure.