Always tired? A blood test can help find out why
Feeling exhausted all the time — even after a full night's sleep — is one of the most common reasons people see a doctor, and one of the most common reasons people put off doing anything about it. It's easy to assume tiredness is just 'life' — work, kids, stress — and often it is. But persistent, unexplained fatigue can also have a treatable biochemical cause that a simple blood test can help identify.
Some of the most common blood-testable causes of tiredness are an underactive thyroid, low iron, low vitamin B12 or folate, low vitamin D, and blood sugar problems. Each of these is common, each is checkable in a single blood draw, and each is manageable once identified.
This page explains what a blood test can check for fatigue, and which of our panels are the sensible starting point — so you can get a clear, clinician-reviewed answer instead of guessing.
Common blood-testable causes
Underactive thyroid
An underactive thyroid (hypothyroidism) slows down your metabolism and is a common, very treatable cause of tiredness, weight gain and feeling the cold. A thyroid blood test checks TSH, FT4, FT3 and thyroid antibodies.
Check with Thyroid Profile →Low iron
Low iron is one of the most frequent reasons for fatigue, particularly in women with heavy periods and people on plant-based diets. An iron panel can spot a deficiency before it progresses to anaemia.
Check with Iron Status →Vitamin B12, folate or vitamin D deficiency
Low B12, folate or vitamin D can all cause tiredness, low mood and muscle weakness, and are easily corrected once identified with the right dose rather than guesswork.
Check with TATT (Tired All The Time) →Blood sugar imbalance
Raised blood sugar or early insulin resistance can leave you feeling drained, especially after meals. HbA1c and glucose testing can help identify or rule this out.
Check with Diabetes Status →Panels worth considering
TATT (Tired All The Time)
Our number-one panel for people who are constantly exhausted. Checks all the common culprits in one blood draw — thyroid, iron, B12, vitamin D and inflammation.
Iron Status
This panel measures 6 markers to map both your iron stores and how efficiently iron moves around your body.
Thyroid Profile
Your thyroid controls your energy, weight and mood. This panel checks all four key thyroid markers — much more thorough than a standard NHS TSH-only test.
Common questions
What blood tests check for tiredness and fatigue? +
The most common causes of persistent tiredness can be screened with a full blood count (anaemia), ferritin (iron stores), thyroid function (TSH, FT4, FT3), vitamin D, B12, folate, and HbA1c (blood sugar). Our TATT (Tired All The Time) panel covers all of these in one appointment.
Do I need to fast before a fatigue blood test? +
Most of the markers involved don't require fasting. Because some panels include glucose and HbA1c, we may ask you to avoid eating for a few hours if your appointment is in the morning — we'll confirm any preparation when you book.
Will a blood test definitely explain my tiredness? +
A blood test is a sensible first step and can identify or rule out several common, treatable causes. It doesn't cover every possible cause of fatigue, and a clinician reviews your results alongside your symptoms to advise on sensible next steps.
Get a clear, clinician-reviewed answer
Same-week appointments. No GP referral. Prompt results, reviewed by a clinician.
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