You go to bed at a reasonable hour, you get your seven or eight hours, and you still wake up feeling as if you have not slept. The slump arrives before lunch, weekends do not refill the tank, and “have you tried an early night?” stopped being useful advice a long time ago.
Being tired all the time, often shortened to TATT in general practice, is a common reason people ask about a blood test. It can also be frustrating to investigate, because the symptom is real, it affects everything, and a basic blood panel often comes back unremarkable.
Sometimes there is a clear, treatable cause, and a blood test can help to check for some of the common ones. A blood test is information, not a diagnosis: results need to be read in context, alongside your symptoms, history and examination. This guide covers why more sleep does not always help, what your blood can and cannot show, when to see your GP, and how to get tested. At WMG Health, our private blood testing service on Harley Street, London, your results are reviewed by a GMC-registered doctor and no GP referral is needed.
Why more sleep does not fix it
Clinicians separate two things most of us lump together:
- Tiredness is a normal response to too little sleep, exertion or short-term stress. It improves with rest.
- Fatigue is persistent exhaustion that does not resolve with rest, drains motivation as well as energy, and gets in the way of daily life.
(These are everyday definitions rather than strict medical ones.)
If rest is not helping, the cause may not be the amount of sleep. Possibilities include poor-quality sleep, stress or low mood, or a medical cause such as iron deficiency, an underactive thyroid or a B12 deficiency. Some of these can be checked with a blood test.
Persistent fatigue often comes with other features, such as unrefreshing sleep, brain fog, reduced exercise tolerance, low mood or reduced libido. None of these is specific to one cause: they overlap between iron deficiency, thyroid problems, sleep disorders, low mood and many other conditions, so they cannot tell you the cause on their own. The NHS advises seeing a GP if you have felt tired for a few weeks and do not know why, or if tiredness is affecting your daily life. Our persistent fatigue page summarises the checklist.
The treatable causes a blood test can find
The NHS links ongoing tiredness to a familiar list of causes: poor sleep, stress and depression, an unhealthy lifestyle, hormonal changes, infections such as glandular fever and COVID-19, some medicines, and conditions including iron deficiency anaemia, diabetes, thyroid problems, sleep apnoea and ME/CFS. A blood test can help to check some of these.
Iron deficiency (low ferritin)
Ferritin reflects your iron stores. Stores can run low before anaemia shows up, and a normal full blood count does not rule out iron deficiency: around half of people with iron deficiency have a normal red cell size (MCV). UK guidance generally treats a ferritin below 30 µg/L as indicating low iron stores, although laboratory cut-offs vary, and ferritin can read falsely normal when there is inflammation. Typical symptoms include tiredness, shortness of breath, palpitations and paler skin. Our guide to what low ferritin feels like covers it in full.
If your iron is low, finding out why matters. Heavy periods and pregnancy are common causes, but slow bleeding from the gut is another, and that needs a doctor’s assessment, particularly in men and in women after the menopause. Please speak to your GP about the cause before starting iron tablets.
Thyroid problems
The NHS lists an underactive thyroid as a cause of extreme tiredness, weight gain, feeling cold, low mood and difficulty concentrating. An overactive thyroid can also cause ongoing tiredness and weakness, alongside trouble sleeping, anxiety, a fast or irregular heartbeat and weight loss. TSH is the usual first test. NICE guidance (NG145) says free T4 is added to the same sample if TSH is high, and free T4 and free T3 if TSH is low. See our thyroid blood test page and our guide to underactive and overactive thyroid tests.
Vitamin D deficiency
Low vitamin D is common in the UK: from about October to early March, sunlight is not strong enough for the body to make it. A level below 25 nmol/L is generally classed as deficient, 25 to 50 nmol/L may be inadequate for some people, and above 50 nmol/L is sufficient for almost everyone. Significant deficiency can cause bone pain. Tiredness and low mood are often reported alongside low levels, but vitamin D is only one of many possible causes, and the evidence that supplements relieve fatigue in the wider population is limited, so a low result should not be assumed to explain how you feel. The NHS advises that everyone should consider a daily 10 microgram supplement in autumn and winter. See our guide to vitamin D deficiency symptoms.
Vitamin B12 and folate deficiency
Both are needed to make red blood cells and to keep nerves working properly. The NHS lists extreme tiredness, a lack of energy, pins and needles, mouth ulcers, a sore tongue, and problems with memory and concentration as possible signs, and deficiency can lead to anaemia. Causes include pernicious anaemia (the most common cause in the UK), a vegan diet without supplements or fortified foods, some medicines such as proton pump inhibitors (for example omeprazole), and long-term metformin, which the MHRA says can commonly reduce B12 levels. Older people are affected more often. If you have pins and needles, see your GP promptly, because some of the problems caused by deficiency can be permanent if it is not treated early.
Raised blood sugar
Feeling very tired is one of the most common symptoms of type 2 diabetes, usually with needing to pass urine more often, constant thirst or losing weight without trying, although some people have no symptoms. HbA1c shows average blood glucose over the previous two to three months and is the main blood test used to diagnose diabetes and pre-diabetes. Diabetes is confirmed by a clinician, and an HbA1c result at or above the diabetes threshold needs follow-up with your GP. Our HbA1c guide explains what the number means.
Inflammation, infection, kidneys and liver
A raised CRP or ESR is a non-specific sign of inflammation or infection. It cannot tell you the cause, and it needs interpreting by a clinician alongside your symptoms. Glandular fever can leave tiredness lasting for several months, and long COVID (symptoms lasting more than 12 weeks) commonly includes extreme tiredness. Kidney and liver problems can also contribute to fatigue, and kidney and liver tests are part of the usual initial work-up when no cause is obvious.
Hormonal causes
In men, low testosterone can be associated with tiredness, low mood and reduced libido, but these symptoms are non-specific and many men who have them have normal levels. Our guide to low testosterone symptoms in men describes the pattern, and a testosterone blood test needs a morning sample, drawn between 8am and 10:30am, to be meaningful. In women in their 40s and 50s, perimenopause can cause low mood, brain fog and disturbed sleep, which can in turn leave you exhausted. NICE says that in otherwise healthy women aged 45 or over with typical symptoms, perimenopause can be diagnosed from symptoms alone, without a blood test, so testing is most useful for checking other causes of tiredness; our guide to perimenopause and when a blood test helps explains why.
What a blood test cannot see
Some of the most common reasons for being “always tired despite eight hours in bed” do not show up on bloodwork at all.
- Obstructive sleep apnoea is a recognised cause of daytime tiredness. The NHS lists loud snoring, breathing that stops and starts during sleep (often noticed by a partner), gasping, snorting or choking noises, frequent waking and morning headaches. It is assessed through a sleep study arranged by a specialist, not by a blood test, so see your GP if these sound familiar.
- Stress, mood and lifestyle. Stress, depression, poor sleep and an unhealthy lifestyle are all listed by the NHS as causes of tiredness, and they can sit alongside a measurable cause.
- Seasonal tiredness. If your tiredness arrived with the autumn, shorter days and less sunlight may play a part. If it is lasting for weeks and affecting daily life, it is still worth speaking to your GP.
- ME/CFS and long COVID. NICE guideline NG206 says ME/CFS can be suspected after about six weeks in adults and is diagnosed when symptoms have persisted for three months and are not explained by another condition. A key feature is feeling much worse after physical or mental effort. The NHS says there is no test for ME/CFS: blood tests are used to rule out other conditions such as anaemia, an underactive thyroid, or liver and kidney problems. The NHS describes long COVID as symptoms lasting more than 12 weeks, and it is likewise assessed by a clinician rather than diagnosed from a single blood test.
What a complete fatigue blood test includes
A broad panel checks several of the common, treatable causes in one sample, rather than testing one suspect at a time. It cannot cover every cause of fatigue.
| Marker | Why it is checked | In General Wellness (£279)? |
|---|---|---|
| Full blood count | Anaemia, infection and platelets | Yes |
| Iron studies, including ferritin | Iron handling and stores | Yes |
| Vitamin D | Vitamin D status | Yes |
| Vitamin B12 | B12 status | Yes |
| Thyroid function (TSH, FT3, FT4) | Under- or overactive thyroid | Yes |
| CRP and ESR | Inflammation | Yes |
| Zinc | Immunity, hormones and tissue repair | Yes |
| Folate | Works with B12 in red cell production | Yes |
| HbA1c | Diabetes and pre-diabetes | Yes |
| Kidney function (urea and electrolytes) | Kidney filtration and salt balance | Yes |
| Liver function tests | Liver health | Yes |
| Calcium and magnesium | Mineral and metabolic balance | Can be added |
Where a marker says “can be added”, a clinician can include it through a custom panel, with the price confirmed in writing before booking. If you have gut symptoms or an unexplained iron or B12 deficiency, ask your GP whether a coeliac blood test is appropriate.
The General Wellness panel (£279) is a broad starting point, and it also includes a lipid profile (cholesterol). The right panel shifts with your other symptoms:
- With hair shedding: Hair Loss Essentials (£249) covers ferritin and iron studies, vitamin D, B12, folate, thyroid function (TSH, FT3, FT4), a full blood count, zinc and CRP.
- With low libido, mood change or hair changes: The Hormone Specialist (£299) covers DHT, total testosterone, SHBG, LH, FSH, prolactin, oestrogen (oestradiol), thyroid function (TSH, FT3, FT4), zinc and CRP.
- Men with signs of low testosterone: the Testosterone Panel (£199) measures total and free testosterone, SHBG, LH, FSH and DHT.
- After thyroid and iron have been checked: the Adrenal Function Panel (£299) measures morning cortisol and DHEA-sulfate, with total testosterone and SHBG, and the blood must be drawn between 8am and 9am. Our adrenal blood test guide explains when it is worth it.
Why “normal” results can miss the cause
The complaint we hear most often is: “My GP said my bloods were normal, but I still feel exhausted.” Usually one of two things is going on.
- The relevant tests may not have been run. A first-line check may not have included ferritin, vitamin D or B12, in which case those have not been ruled out. Which tests a GP requests depends on your symptoms and national guidance.
- A result just inside the range can still be a grey area. For ferritin, UK guidance treats below 30 µg/L as low iron stores, but the British Society of Gastroenterology suggests 45 µg/L as a cut-off that balances sensitivity and specificity, and NHS Scotland guidance says values of 30 to 50 µg/L can still be consistent with iron deficiency, particularly in older people or when there is inflammation. A borderline result needs interpreting alongside your symptoms and other tests, and whether it needs treatment is a decision for a clinician.
This is why results are best read by a clinician alongside your symptoms, rather than as a list marked normal or abnormal.
When to see your GP or seek urgent care
A private blood test is not a substitute for a doctor’s assessment, and it does not diagnose anything on its own. Book a GP appointment if you have felt tired for a few weeks and do not know why, or if tiredness is affecting your daily life. See your GP promptly if tiredness comes with unexplained weight loss, night sweats, a fever that keeps coming back, swollen glands or a new lump, blood in your stool or urine, constant thirst and passing more urine than usual, numbness or weakness, or pins and needles. Take any abnormal result to your GP.
Call 999 if you have chest pain that is tight or squeezing or spreads to your arms, neck or jaw, severe difficulty breathing, or if someone collapses. Use NHS 111 for urgent advice if you are worried about new symptoms such as breathlessness at rest or fainting and it is not an emergency. If you are feeling very low or having thoughts of harming yourself, call NHS 111 or the Samaritans on 116 123 at any time, or call 999 or go to A&E if you may be in immediate danger.
Getting tested at WMG Health
A fatigue blood test may be worth considering if your tiredness has lasted several weeks and is not improving with rest, if earlier bloods were normal but you still feel exhausted, if you have not fully recovered from a viral illness, or if you are in your 40s and wondering whether hormones are contributing.
Your blood is drawn at 134 Harley Street, and results are released as each marker is reviewed by a GMC-registered doctor, with the expected timeframe confirmed at booking. Anything that needs follow-up is flagged, and our clinical team can advise on the next step, such as taking your results to your GP.
Common questions
Why am I always tired even though I sleep eight hours? Because the cause may not be the amount of sleep. Poor sleep quality (for example sleep apnoea), iron deficiency, thyroid problems, B12 deficiency, raised blood sugar, stress and low mood can all leave you exhausted however long you spend in bed.
Do I need to fast for a fatigue blood test? It depends on the panel. For the General Wellness panel, fast for at least 12 hours beforehand, but not much longer than 12 hours. Water is fine, and encouraged, but no food or other drinks, and do not stop prescribed medication. Do not take iron tablets for 24 hours or a B12 supplement beforehand, and if you take folate, B-complex or multivitamin supplements, hold them for 24 to 72 hours before testing. If you take thyroid tablets, take them after the blood draw, not before. Hair Loss Essentials also requires a fast of at least 12 hours. For the hormone panels, fasting is preferred but not essential, and the blood must be drawn in a set morning window: the Testosterone Panel between 8am and 10:30am, and the Adrenal Function Panel between 8am and 9am. Your booking confirmation will give the instructions for your panel.
What if everything comes back normal? A normal panel is reassuring about the markers that were tested, but it does not rule out every cause of fatigue. It can help point the next step towards sleep, mood, lifestyle or post-viral recovery, and if your symptoms persist you should see your GP. Our clinical team can advise on what to do next.
Do I need a GP referral? No. WMG Health is direct-access, so you can book online or by phone on 020 3239 3378.
Sources
- NHS: Tiredness and fatigue; Iron deficiency anaemia; Vitamin B12 or folate deficiency anaemia; Underactive thyroid; Overactive thyroid; Sleep apnoea; Type 2 diabetes symptoms; Vitamin D; ME/CFS diagnosis; Long COVID; Glandular fever; Heart attack; Help for suicidal thoughts. nhs.uk
- NICE Guideline NG145: Thyroid disease: assessment and management. nice.org.uk
- NICE Guideline NG206: Myalgic encephalomyelitis (or encephalopathy)/chronic fatigue syndrome: diagnosis and management. nice.org.uk
- NICE Guideline NG23: Menopause: identification and management, and Quality Standard QS143. nice.org.uk
- British Society of Gastroenterology: Guidelines for the management of iron deficiency anaemia in adults (Snook et al, Gut 2021). bsg.org.uk
- NHS Highland: Iron deficiency guidelines (Right Decisions, NHS Scotland). rightdecisions.scot.nhs.uk
- MHRA Drug Safety Update: Metformin and reduced vitamin B12 levels: new advice for monitoring patients at risk. gov.uk
- Diabetes UK: Diabetes test: how to test for diabetes. diabetes.org.uk
- Royal Osteoporosis Society: Vitamin D and bone health: a practical clinical guideline for patient management. theros.org.uk
This article is for general information only. It is not medical advice and is not a diagnosis. If you have concerns about persistent fatigue, speak to your GP, or book an appointment with us.