When is blood test recommended for chronic fatigue syndrome?

Chronic fatigue syndrome, also called myalgic encephalomyelitis, does not have one blood test that confirms it. A clinician may use blood tests to look for clues such as anaemia, thyroid problems, inflammation, infection, diabetes, or nutritional deficiencies. The choice depends on your symptoms, examination, medicines, diet, and medical history. Results can be normal even when fatigue is severe. A diagnosis is based on the overall pattern, including activity-related worsening and sleep or concentration problems, after other explanations have been considered.

Arrange an appointment if fatigue persists, limits daily activities, or follows an illness without improving. Write down when it began, what makes it worse, sleep changes, dizziness, pain, bowel symptoms, weight change, and all medicines or supplements. Do not stop prescribed treatment before the appointment. Ask whether you should avoid food beforehand; preparation varies by the tests ordered. If the first results do not explain the fatigue, follow-up may involve monitoring symptoms or considering other assessments.

Seek urgent medical help for fatigue with chest pain, severe breathlessness, fainting, new confusion, one-sided weakness, or heavy bleeding. Contact a clinician promptly if you cannot keep fluids down, are becoming rapidly weaker, have persistent fever, or notice unexplained weight loss. These features need assessment on their own and should not be attributed to chronic fatigue syndrome without checking for other causes.

Which causes of fatigue are you checking for? Do I need to fast or change any medicines before the sample? When will the results be reviewed, and what is the next step if they are normal? Could anaemia, thyroid disease, infection, nutrition, sleep, or mood be contributing?