Persistently tired — which tests are worth doing
General Health · 6 min read
Tiredness is one of the most common reasons people visit a GP, and one of the least specific symptoms in medicine. It accompanies almost everything — physical illness, mental health, sleep, medication, stress, and ordinary life.
That makes it frustrating to investigate. It also makes it worth being systematic rather than testing at random.
Before testing anything
A good proportion of persistent tiredness has an explanation that no blood test will find:
- Sleep — quantity, but more often quality. Sleep apnoea is substantially underdiagnosed, particularly in men who snore and wake unrefreshed
- Mental health — depression and anxiety very commonly present as physical exhaustion rather than low mood
- Medication — beta blockers, antihistamines, some antidepressants
- Alcohol — regular drinking disrupts sleep architecture even when it helps you fall asleep
- Under-eating or under-fuelling, particularly in people exercising heavily
If any of those fit, they are worth addressing before or alongside testing.
The two most useful things to check
Iron (ferritin). Low iron is one of the most common nutritional deficiencies in the UK, especially in women of menstruating age, vegetarians, vegans and endurance athletes. Ferritin — the stored form of iron — falls before haemoglobin does, so it flags a problem earlier than a standard anaemia test. Alongside tiredness it often causes breathlessness on exertion, pale skin, brittle nails and poor concentration.
Thyroid (TSH). An underactive thyroid develops gradually and its symptoms are easy to attribute to other things: tiredness, weight gain, feeling cold, dry skin, low mood, constipation. TSH rises before thyroid hormones fall, which makes it the earliest marker.
Both can be screened at home, and both are also standard GP blood tests.
Other things a GP may consider
Depending on your history, a GP might check full blood count, vitamin B12 and folate, vitamin D, blood glucose or HbA1c, kidney and liver function, and coeliac serology. Coeliac disease is worth flagging: it presents as unexplained tiredness surprisingly often, without obvious digestive symptoms.
When not to bother testing, and see a GP instead
Some things need a person, not a test:
- Tiredness with unexplained weight loss
- Tiredness with a lump, persistent pain, or night sweats
- Sudden or severe onset, rather than gradual
- Tiredness that stops you doing normal daily activities
- Any tiredness that persists beyond a few weeks without explanation
A realistic expectation
Many people who investigate persistent tiredness find every test comes back normal. That is a genuinely common outcome and it does not mean the tiredness is imagined. It usually shifts the focus toward sleep, mood, stress and recovery — which are harder to measure but more often the answer.
Common questions
What blood tests are most useful for persistent tiredness?
Ferritin (stored iron) and TSH (a thyroid marker) are generally the two most useful starting points, since low iron and an underactive thyroid are common causes of fatigue that build gradually.
Could my tiredness be caused by something other than a medical condition?
Often, yes. Poor sleep quality, stress, low mood, certain medications and alcohol can all cause persistent tiredness without any abnormal blood test result, and it's worth thinking about these before or alongside testing.
When should I see a GP rather than relying on home testing?
See a GP if tiredness comes with unexplained weight loss, a lump, persistent pain, night sweats, a sudden or severe onset, or if it's stopping you doing normal daily activities.
What does it mean if all my test results come back normal but I'm still tired?
This is a genuinely common outcome and doesn't mean the tiredness isn't real. It often points toward sleep, stress or mood as contributing factors, which are worth discussing with a GP even though they don't show up on a blood test.
Can coeliac disease cause tiredness without digestive symptoms?
Yes, unexplained tiredness is a recognised way coeliac disease can present, sometimes without obvious digestive symptoms, which is why a GP may consider coeliac screening as part of investigating persistent fatigue.