Always Tired? Blood Tests That Could Help Find The Cause
6-minute read · Reviewed by the Veritas Clinical Team · Last updated July 2026
If you’ve been told to “get some blood tests done” for ongoing tiredness, it’s fair to ask which ones actually matter. There’s no single “tiredness test”, different blood tests check completely different things, so knowing what each one covers makes it much easier to choose where to start.
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“I’ve been told to just get some tests done for my tiredness, but nobody’s told me which ones. Where do I even start?”
A completely fair question. Blood tests for fatigue aren’t one-size-fits-all, they’re chosen based on your symptoms and history, which is exactly what a pharmacist consultation is for.
Ordering every possible test isn’t usually the best approach, some results can be misleading without the right context, and it isn’t cost-effective either. A short conversation about your symptoms first usually narrows things down to two or three tests that are actually worth doing.
General guidance on the clinical assessment of fatigue.Why test instead of guess?
Tiredness itself doesn’t tell you much on its own, it’s one of the most common, nonspecific symptoms there is. A blood test replaces guesswork with an actual number, which either points toward a clear, often treatable cause, or rules one out so you can look elsewhere with more confidence.
One blood test can cover tiredness in general.
There’s no single “fatigue test.” Iron, vitamin D, thyroid function, blood sugar, and stress hormones are all measured separately, and each one tells you about a different system in your body.
Not sure where to start?
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The blood tests that can help
Ferritin (iron stores)
Low iron reserves can cause fatigue even before anaemia develops.
Vitamin D
Rapid results, particularly relevant over autumn and winter.
Thyroid function
An underactive thyroid commonly causes tiredness and weight changes.
HbA1c (blood sugar)
Reflects your average blood sugar over roughly three months.
Testosterone
May be relevant depending on your symptoms and history.
Cortisol
Your body’s main stress hormone, sometimes relevant to persistent fatigue.
Vitamin B12 deficiency is another common contributor to tiredness. Rather than a standalone test, our pharmacists assess this through your symptoms and history, and can advise whether a B12 injection or a formal blood test through your GP is the more appropriate next step.
Several of these tests, including vitamin D and HbA1c, are rapid tests at Veritas, meaning you get a result far faster than a standard test sent away to a lab. Others, like a full thyroid panel, still need to go to a laboratory, so turnaround times vary by test, your pharmacist will confirm what to expect for each one.
Choosing the right test
These extra clues help point toward which one or two tests are most likely to be useful.
A broader starting combination, such as ferritin, vitamin D and thyroid, may be a sensible first step.
What your results actually mean
A result sitting just outside a “normal” range doesn’t automatically explain your tiredness, and a result within range doesn’t always rule things out completely either. Reference ranges are a guide, not a strict cut-off, which is why your pharmacist interprets your result alongside your symptoms, rather than the number alone.
Can I just choose exactly which tests I want?
Yes, though your pharmacist will usually talk through your symptoms first to help make sure you’re choosing tests likely to actually be useful.
Do I need to fast before these tests?
It depends on the test, HbA1c and cortisol sometimes have specific timing requirements, others don’t. Your pharmacist will confirm what applies when you book.
What happens at your appointment?
A conversation about your symptoms, timeline, and any other health history.
Agreeing which test or tests make the most sense for you.
A straightforward blood sample.
In plain terms, alongside your symptoms, not just as a number.
Treatment where appropriate, or a referral if further investigation is needed.
When should you seek medical advice?
Booking a blood test for ongoing tiredness is usually a routine matter. The following is a general guide to how urgently to act.
- Tiredness lasting several weeks without an obvious cause
- Wanting a baseline check even without other symptoms
- Tiredness alongside unexplained weight change or persistent low mood
- Symptoms that are gradually getting worse rather than staying the same
- Chest pain, severe breathlessness, or fainting
- Significant unexplained weight loss, or coughing up blood
- Severe low mood, or thoughts of harming yourself
These symptoms need assessment by a GP, NHS 111, or A&E as appropriate. If you’re having thoughts of harming yourself, you can also contact the Samaritans free, any time, on 116 123.
How Veritas Pharmacy can help
Our full range of rapid blood tests
Browse everything available in one place.
Hormone testing hub
Testosterone, thyroid, cortisol and more.
Private pharmacist consultation
Talk through your symptoms before choosing a test.
- There’s no single blood test for tiredness, each one checks something different.
- Ferritin, vitamin D, thyroid, HbA1c, testosterone and cortisol are the most relevant options.
- A short consultation first usually narrows things down to just one or two tests.
- Results are interpreted alongside your symptoms, not as a number in isolation.
Related reading
Why am I always tired? Common health issues affecting men
Vitamin D deficiency: 12 signs you shouldn’t ignore
Understanding your HbA1c
Not sure which test is right for you?
Tell us how you’ve been feeling and we’ll help you choose a sensible starting point, without booking tests you don’t need.
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The information in this post is for general information purposes. It is not intended to replace medical advice from a healthcare professional. We make an effort to keep the content on this page up to date and accurate.
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