between appointments · 6 min
Which tests to take for persistent fatigue
In short: for persistent fatigue a GP usually starts with a complete blood count, ferritin, TSH and glucose, then decides based on your symptoms. Don't take every test at once: first tell the doctor how long you have been tired and when it is worse.
Where it usually starts
Most often a GP orders a complete blood count, ferritin, TSH (the hormone used to check how the thyroid is working) and glucose. These cover common causes of fatigue: anaemia and low iron, thyroid function and blood sugar.
Sometimes a blood chemistry panel, vitamin B12 or vitamin D is added. Which tests you need is up to the doctor, based on your symptoms and history: there is no single list for everyone.
Not just tests
Fatigue is often about sleep, workload and stress rather than illness. For a couple of weeks before the appointment, note how much you sleep, when you are most tired and what helps.
Tell the doctor about the medicines you take: some cause drowsiness and weakness. And about your mood: low mood and anxiety often show up as tiredness too.
When to see a doctor straight away
Don't put off the visit if fatigue comes with unexplained weight loss, fever, night sweats, breathlessness or chest pain.
With sudden severe weakness, confusion or severe chest pain, call 103 or 112.