- 01Normal blood tests are expected in ME/CFS
Blood tests in suspected ME/CFS exist to find the other conditions that cause fatigue. A normal panel rules those out; it does not rule ME/CFS out or mean nothing is wrong.
Being tired for months is common; ME/CFS is narrower. Its defining feature is post-exertional malaise (PEM): a crash in symptoms that comes hours or a day after physical, mental or emotional effort and can last days 1. About 1.3% of US adults reported ME/CFS in a 2021 to 2022 national survey, women (1.7%) more often than men (0.9%) 6. In people with ME/CFS, routine blood tests usually come back normal 3, and that is the expected result, because the tests are there to find other conditions that cause the same fatigue.
If you are tired all the time but have no crash after effort, start with our page on fatigue, which covers the far more common causes. Chronic fatigue is a symptom; chronic fatigue syndrome is an illness with the specific pattern below.
Chronic fatigue syndrome symptoms
The Institute of Medicine (IOM, now the National Academy of Medicine) set out the criteria most US clinicians use. ME/CFS requires all three core symptoms plus at least one of the two extras 1.
| Symptom | Required? | What it looks like |
|---|---|---|
| Big drop in activity with fatigue for more than 6 months | Yes | Fatigue that is new, not caused by ongoing effort, not relieved by rest, and that cuts work, school or social life well below pre-illness levels |
| Post-exertional malaise | Yes | Symptoms worsen after effort that used to be easy, often with a delay |
| Unrefreshing sleep | Yes | Waking as tired as when you went to bed, even after a full night |
| Cognitive impairment (brain fog) | One of these two | Slow thinking, poor memory, trouble finding words |
| Orthostatic intolerance | One of these two | Symptoms worsen when standing or sitting upright and ease when lying down |
Many people also have muscle or joint pain, headaches, a sore throat, tender lymph nodes, sensitivity to light, sound or smells, and trouble regulating temperature. ME/CFS symptoms fluctuate from week to week, which is one reason people are told they look fine on a good day. Our pages on brain fog, dizziness and poor sleep cover those symptoms in their own right.
ME/CFS is a serious, chronic, complex, and multisystem disease that frequently and dramatically limits the activities of affected patients.
Post-exertional malaise: the crash after effort
Post-exertional malaise is a worsening of fatigue, pain, brain fog and flu-like feelings after effort that a person could once handle. The trigger can be a walk, a long conversation, a stressful meeting or a busy day. The crash is often delayed by hours or a day or more, and it can last days to weeks 1. Because of that delay, people often blame the wrong day and keep repeating the pattern.
PEM also shows up in testing. On a two-day cardiopulmonary exercise test (two exercise tests 24 hours apart), people with ME/CFS often perform worse on day 2, while healthy people repeat their day 1 result 3. The test is not required for diagnosis and can itself trigger a crash, so it is used selectively.
How doctors diagnose ME/CFS
ME/CFS is diagnosed by history and examination against a set of criteria, after other causes have been looked for. The two current definitions differ mainly on timing.
| IOM 2015 (US) 1 | NICE NG206 2021 (UK) 2 | |
|---|---|---|
| How long symptoms must last | More than 6 months | Suspect at 6 weeks in adults (4 weeks in children); confirm after 3 months |
| Post-exertional malaise | Required | Required |
| Unrefreshing sleep | Required | Required |
| Brain fog | Brain fog or orthostatic intolerance required | Required |
| Role of blood tests | Exclude other illness | Exclude other illness, with a listed baseline set |
A simple 10-minute standing or lean test, where a clinician tracks heart rate and blood pressure while you stand still, can document orthostatic intolerance in an ordinary clinic 3. An older 1994 definition, the Fukuda criteria, did not require PEM, so older studies included a broader group 7.
The blood tests that rule out look-alikes
This is the standard blood test for fatigue that has lasted months. NICE lists a baseline set to exclude other diagnoses before ME/CFS is confirmed: urinalysis (a urine dip test), full blood count, kidney function and electrolytes, liver function, thyroid function, ESR or CRP (two blood tests for inflammation), calcium and phosphate, HbA1c, ferritin, celiac screening and creatine kinase (an enzyme that leaks from damaged muscle) 2. Each one is there because an abnormal result points to a treatable condition that causes fatigue.
| Test | An abnormal result points toward |
|---|---|
| Complete blood count, hemoglobin | Anemia, infection, or a blood disorder (see CBC explained) |
| Ferritin | Iron deficiency, even before hemoglobin falls |
| TSH and free T4 | Hypothyroidism, often from Hashimoto's disease (see reading your thyroid panel) |
| HbA1c or glucose | Diabetes, most often type 2 |
| CRP or ESR | Inflammation, infection or autoimmune disease such as lupus; see high CRP |
| tTG-IgA (celiac antibody test) | Celiac disease, which can cause fatigue with few gut symptoms |
| Kidney panel (creatinine, eGFR, sodium, potassium) | Kidney disease or an electrolyte problem; eGFR is an estimate of kidney filtering. Low sodium and high potassium together can point to adrenal failure |
| Calcium | Parathyroid or bone disease (overactive parathyroid); see high calcium |
| Creatine kinase | Muscle disease or inflammation |
| Liver tests | Liver disease such as fatty liver, including high AST or high bilirubin |
| Morning cortisol (if suspected) | Addison's disease; see low morning cortisol |
| Vitamin B12, folate, vitamin D (when relevant) | B12 deficiency, folate deficiency, vitamin D deficiency |
Any result outside its reference range should be reviewed with the clinician who ordered it before ME/CFS is considered, because it points to a different, often treatable, diagnosis.
Read these first when fatigue will not lift
Conditions that can look like ME/CFS
Beyond the blood-test conditions above (hypothyroidism, anemia, celiac disease, Addison's disease, lupus), four common conditions overlap with ME/CFS.
| Condition | Overlap with ME/CFS | How it differs |
|---|---|---|
| Sleep apnea | Unrefreshing sleep, daytime exhaustion | Shown on a sleep study |
| Chronic fatigue syndrome vs depression | Fatigue, low motivation | People with depression often feel better after activity; people with ME/CFS feel worse a day later 3 |
| Chronic fatigue syndrome vs fibromyalgia | Pain, fatigue, poor sleep | Fibromyalgia centers on widespread pain; the two often co-exist |
| POTS (postural orthostatic tachycardia syndrome) | Symptoms worse on standing | A large heart-rate rise on a stand test; often co-exists with ME/CFS |
What causes ME/CFS?
No single cause has been found. ME/CFS often begins after an infection such as Epstein-Barr virus (the cause of glandular fever, or mono) or a flu-like illness, and some people with long COVID develop a pattern that meets ME/CFS criteria 3. A detailed NIH study that measured many body systems in 17 people with ME/CFS that began after an infection found differences in immune cells, autonomic function (the nervous system that controls heart rate and blood pressure), brain activity during effort, and lower levels of breakdown products of catecholamines (chemical messengers such as dopamine and noradrenaline) in the fluid around the brain and spine 4.
Treatment and day-to-day management
There is no cure and no approved drug for ME/CFS 3. Management centers on pacing: learning your energy envelope (how much activity you can do without triggering a crash) and staying within it, with rest planned before you need it. NICE reversed its earlier advice in 2021 and says not to offer graded exercise therapy 2.
Do not offer people with ME/CFS ... any programme that ... uses fixed incremental increases in physical activity or exercise, for example, graded exercise therapy.NICE guideline NG206, recommendation 1.11.14 (2021) 2
NICE also says cognitive behavioral therapy may help some people cope but should not be presented as a cure 2. The rest of care treats what can be treated: sleep problems, pain, and orthostatic intolerance, where a clinician may suggest fluids, salt or compression garments 3. Raising salt is not right for everyone, especially people with high blood pressure or kidney or heart disease, so that decision belongs with a doctor.
Only if a test shows you are low
Strong evidence, if deficientIronCorrecting a measured iron deficiency can ease the fatigue it causes. A low ferritin in an adult also needs its cause found by a clinician, for example blood loss from the gut. ME/CFS itself needs separate care.In our shop 
No supplement treats ME/CFS. Iron in particular should only be started after a ferritin test and a clinician's advice, because excess iron builds up in the body. If a test shows low magnesium, see magnesium deficiency.
Will I get better?
The course of ME/CFS varies. Children and teenagers recover more often than adults 5. A systematic review found a median full-recovery rate of about 5% in adults, with improvement far more common than full recovery 5, and the IOM reports that at least a quarter of people with ME/CFS are housebound or bedbound at some point 1. Tracking symptoms and repeat blood results over months shows more than any single visit; see why trends beat single readings.
Chest pain, severe breathlessness or fainting needs emergency care: call 911. Fatigue with unintentional weight loss, fevers or night sweats, new weakness or numbness, or blood in stool or vomit needs prompt medical care, whether or not ME/CFS is suspected. If you are having thoughts of self-harm, call or text 988 (US Suicide & Crisis Lifeline).
Citations
- Institute of Medicine (2015). Beyond Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: Redefining an Illness. National Academies Press.
- NICE (2021). NG206: Myalgic encephalomyelitis (or encephalopathy)/chronic fatigue syndrome: diagnosis and management.
- Bateman L et al. (2021). Myalgic encephalomyelitis/chronic fatigue syndrome: essentials of diagnosis and management. Mayo Clinic Proceedings.
- Walitt B et al. (2024). Deep phenotyping of post-infectious myalgic encephalomyelitis/chronic fatigue syndrome. Nature Communications.
- Cairns R, Hotopf M (2005). A systematic review describing the prognosis of chronic fatigue syndrome. Occupational Medicine.
- Vahratian A, Lin J-MS, Bertolli J, Unger ER (2023). Myalgic encephalomyelitis/chronic fatigue syndrome in adults: United States, 2021-2022. NCHS Data Brief No. 488.
- Fukuda K et al. (1994). The chronic fatigue syndrome: a comprehensive approach to its definition and study. Annals of Internal Medicine.
Educational context only, not medical advice or a diagnosis. Always discuss your results with a clinician.
