Tired all the time: is it anaemia, thyroid trouble or something else?

The NHS lists sleep problems, stress, medicines and several health conditions among possible reasons for fatigue. Anaemia may also come with breathlessness or noticeable heartbeats; an underactive thyroid may come with feeling unusually cold, dry skin or weight change. The NIDDK cautions that fatigue and weight gain are common and do not necessarily mean a thyroid condition. None of these combinations proves a cause in one person.

For a few days, note when the tiredness began, whether you feel sleepy enough to doze or simply lack energy, and which tasks have become harder. Add sleep, breathlessness, heavy bleeding if relevant, thirst, temperature sensitivity, mood and any new medicines. The aim is not to match yourself to a disease checklist. It is to give a clinician a clearer history than ‘I am always tired’.

A clinician may use a full blood count to look at blood cells and haemoglobin when anaemia is a possibility. Thyroid function needs different blood tests. The NHLBI and NIDDK both describe assessment as a combination of history, examination and suitable tests; neither condition can be confirmed by fatigue alone. Ask which test fits your history, what the result would mean, and whether another test or follow-up is needed.

Do not start high-dose iron because tiredness sounds like anaemia. Not every anaemia is due to low iron, and the NHLBI says treatment depends on the cause; excess iron can be harmful. If you already take iron or another supplement, bring its name and dose to the appointment. A result from one lab should also be discussed with the clinician who knows why it was ordered.

Arrange a medical visit if fatigue lasts for weeks without a clear reason, affects everyday life or comes with other changes such as weight loss or mood symptoms. Ask sooner if you are worried or the change is severe. If you develop sudden chest pain that does not go away or severe trouble breathing, seek emergency care rather than waiting for a fatigue test.

Our tiredness guide can help organise sleep, activity and other changes before a non-urgent visit. It does not measure haemoglobin or thyroid hormones and cannot choose a lab test for you. Its value is a better conversation, not a diagnosis hidden in a score.