Always tired? The five blood tests worth asking for

Quick answer: Ask for a full blood count, ferritin, TSH, HbA1c and a coeliac screen. Together they look for anaemia, low iron stores, an underactive thyroid, diabetes and coeliac disease. Most tiredness turns out to be sleep, stress or mood, and routine tests change treatment for only about 1 in 20 people. All five are free through a GP in the UK and with a requisition in Canada.

In this guide

Who this is for — and when to see a clinician first
Most tiredness isn't in your blood
The five tests, and what each one finds
What a clinician may add — and what isn't worth paying for
Getting tested free: US, Canada and UK
Compare your options
What to do next
Common questions
Sources

Who this is for — and when to see a clinician first

This guide is for adults who have felt tired for a few weeks or more without an obvious reason, and who want to know which blood tests are worth asking for. The NHS suggests seeing a GP if tiredness has lasted a few weeks and you can't explain it; the same advice applies to a primary-care clinician in the US or a family doctor or walk-in clinic in Canada.

Book an appointment soon, rather than ordering a kit, if tiredness comes with:

Weight loss you can't explain, fevers or night sweats, swollen glands, frequent infections, or looking unusually pale. NICE's suspected cancer guideline asks GPs to arrange a full blood count within 48 hours when persistent tiredness comes with pallor, fever, repeated infections or swollen glands.
A cough, breathlessness or chest pain if you're 40 or over. The same guideline recommends an urgent chest X-ray.
Loud snoring with gasping or choking in your sleep, or falling asleep during the day. That points to sleep apnoea, which a blood test won't show. In the UK you must tell the DVLA and stop driving if sleepiness affects you.
Low mood, loss of interest, or thoughts of not wanting to be here. If you're thinking about suicide, call or text 988 in the US or 9-8-8 in Canada, or call Samaritans on 116 123 in the UK. If you're in immediate danger, call 999 or go to A&E, or call 911.

Most tiredness isn't in your blood

It's worth knowing the odds before you test. A 2023 review for family doctors in American Family Physician found that blood tests ordered without a specific reason change treatment for only about 5% of people with tiredness. The common causes are things a blood test can't measure: short or poor sleep (nearly 30% of US adults sleep under seven hours a night), stress, depression or anxiety, alcohol, shift work, and side effects of medicines such as antihistamines, beta-blockers and some antidepressants.

That doesn't make testing pointless. The five tests below look for the physical causes that are common, easy to miss and treatable. A normal set of results is useful too: it moves the conversation on to sleep, mood and routine. If low mood or worry is part of the picture, the mental-health support finder shows free routes in your country.

Two non-blood causes deserve a mention. Sleep apnoea is common, often missed and treatable; the AAFP recommends the short STOP-Bang questionnaire, and NICE the Epworth Sleepiness Scale. And if tiredness has lasted six weeks or more, gets worse after physical or mental effort, sleep doesn't refresh you and your thinking is foggy, NICE says ME/CFS should be suspected; it can be diagnosed after three months.

The five tests, and what each one finds

1. Full blood count (FBC or CBC)

Looks for: anaemia — too little haemoglobin to carry oxygen — plus signs of infection and, rarely, blood disorders. The World Health Organization defines anaemia as haemoglobin below 120 g/L (12 g/dL) in women who aren't pregnant and below 130 g/L (13 g/dL) in men. The size of the red cells hints at the cause: small cells suggest low iron, large cells low B12 or folate.

2. Ferritin

Looks for: low iron stores, which can cause tiredness before haemoglobin falls. British Columbia's guideline treats ferritin below 15 µg/L (ng/mL) as diagnostic of iron deficiency, 15–30 as probable, and above 30 as unlikely; the WHO uses below 15 in healthy adults. Ferritin rises with inflammation, so a "normal" result during an infection can hide low stores. Our guide to ferritin and iron explains why ferritin, not serum iron, is the number to ask for.

3. TSH (thyroid-stimulating hormone)

Looks for: an underactive or overactive thyroid. The usual reference range is about 0.4 to 4.0 mU/L, though it varies by laboratory, according to the British Thyroid Foundation. One TSH test is the right first step; Choosing Wisely Canada advises against using free T4 or T3 to screen. Stop biotin supplements, which are common in hair and nail products, two days before the test, as the American Thyroid Association warns they can distort results. More in our thyroid testing guide.

4. HbA1c

Looks for: diabetes or prediabetes, which often cause tiredness before any other symptom. It shows your average blood sugar over about three months, so you don't need to fast. 6.5% (48 mmol/mol) or above is in the diabetes range in all three countries; the prediabetes line is 5.7% in the US and 6.0% (42 mmol/mol) in Canada and the UK. See what your HbA1c number means for the full bands.

5. Coeliac screen (tTG-IgA with total IgA)

Looks for: coeliac disease, an immune reaction to gluten that can cause tiredness and low iron with few gut symptoms. NICE recommends offering the test to anyone with prolonged tiredness. It only works if you're eating gluten: NICE advises gluten in more than one meal every day for at least six weeks before the test. Don't cut out gluten before you're tested.

What a clinician may add — and what isn't worth paying for

A GP or clinic will often add kidney and liver function and an inflammation marker (CRP or ESR); these are part of NICE's list of tests to rule out other causes, and they're cheap. Vitamin B12 is worth adding if you have a risk factor: NICE's 2024 guideline recommends testing when you have a symptom such as tiredness and a risk such as a vegan diet, taking metformin or a stomach-acid medicine, or coeliac or other autoimmune disease. NICE treats total B12 below 180 ng/L (pg/mL) as deficient and above 350 as making deficiency unlikely. British Columbia likewise doesn't support B12 screening without symptoms.

These are often sold for tiredness but aren't worth paying for on that basis alone:

Vitamin D. Choosing Wisely Canada, the Endocrine Society and NICE all advise against routine testing. The NHS recommends a daily 10 µg supplement in autumn and winter without a test. Our vitamin D test guide covers when testing is worthwhile.
Cortisol for "adrenal fatigue". The Endocrine Society says there's no scientific proof that adrenal fatigue is a real condition, and no test can detect it.
IgG food-intolerance tests. The American Academy of Allergy, Asthma & Immunology says they have never been scientifically proven to diagnose food intolerance.
Broad "full body" panels. Choosing Wisely Canada advises against screening blood tests that aren't directly indicated. More markers mean more borderline results to chase, not more answers.

Getting tested free: US, Canada and UK

United States

When a primary-care clinician orders these tests because you're tired, they're billed as diagnostic rather than preventive, so most plans cover them subject to your deductible and co-pay. The ACA's no-cost preventive list includes diabetes screening for some adults with overweight, but not routine anaemia or thyroid screening. Without insurance, federally funded health centers charge on a sliding scale by income. Cash lab prices are often lower than kits: Quest's Fatigue Test Panel costs $159 plus a $6 physician fee and Labcorp OnDemand's Fatigue Test $169. Both include a CBC, ferritin, TSH, HbA1c and kidney and liver tests, but not B12 or a celiac screen, and you give the sample at a lab.

Canada

All five tests are insured when a family doctor, nurse practitioner or walk-in clinic writes the requisition; you take it to LifeLabs, Dynacare or the provincial lab, and results usually appear in your patient portal within days. Vitamin D is the exception: in Ontario, OHIP pays only for listed conditions such as osteoporosis or malabsorption. We found no major home blood-test company that ships these kits to Canada, so the requisition route is the practical one.

United Kingdom

Your GP can order all five free on the NHS. The NHS says a GP may arrange blood tests to check for anaemia, diabetes or thyroid problems; if ferritin or a coeliac screen isn't mentioned, it's reasonable to ask. Results usually appear in the NHS App within about a week. A private kit is mainly useful if you're waiting weeks for an appointment.

Compare your options

Option	Covers	Cost	Limits
GP, primary care or family doctor	All five, plus kidney, liver and B12 when indicated	Free (UK, Canada); US deductible and co-pay usually apply	Needs an appointment; a clinician acts on the result
US community health center	As above	Sliding scale by income	Appointment needed
Quest Fatigue Test Panel (US)	CBC, ferritin, TSH (with free T4 if abnormal), HbA1c, kidney and liver	$159 + $6 fee	No B12 or celiac; lab draw; not in AZ, HI or PR
Labcorp OnDemand Fatigue Test (US)	CBC, ferritin, TSH, HbA1c, kidney and liver	$169	No B12 or celiac; lab draw
Everlywell (US)	Thyroid kit; CBC by lab draw	$149 thyroid; $20 + $15 review for CBC	No single tiredness panel; CBC not in some states

Prices checked 15 October 2026 on each provider's site (Everlywell, Everlywell CBC, LetsGetChecked) and can change. Confirm before buying. For other at-home tests, see compare test kits.

What to do next

Check the list at the top first. Weight loss, fevers, night sweats, breathlessness, choking in your sleep or very low mood need an appointment, not a kit.
Give sleep a fair test. Two weeks of seven to nine hours, less alcohol and a regular wake time is a cheap experiment, and worth mentioning to your clinician either way.
Ask for the five by name: full blood count, ferritin, TSH, HbA1c and a coeliac screen. Add B12 if you're vegan or take metformin or a stomach-acid medicine.
Prepare for the tests. Keep eating gluten, and stop biotin two days before. No fasting is needed unless glucose or cholesterol is added.
If everything is normal, keep going. Ask about sleep apnoea, mood and your medicines, and about ME/CFS if tiredness has lasted six weeks or more and gets worse after effort.

Want a test matched to your symptoms?

The at-home test matcher checks tiredness alongside your other symptoms, flags anything that needs a clinician first, and shows the free route before any kit.

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Common questions

Should I ask for a vitamin D test if I'm always tired?

Usually not. Guidelines in the US, Canada and the UK advise against routine vitamin D testing, and tiredness alone isn't a reason most health systems will pay for it. The NHS suggests a daily 10 microgram supplement in autumn and winter instead. A test makes sense with bone pain, malabsorption or kidney disease.

Do I need to fast before these blood tests?

Not for these five. A full blood count, ferritin, TSH, HbA1c and a coeliac screen can be taken at any time of day. Two things do matter: stop biotin supplements two days before a thyroid test, and keep eating gluten daily for six weeks before a coeliac screen. Fasting is needed only if glucose or cholesterol is added.

My results are all normal. Why am I still tired?

Normal results are the most common outcome, and they're useful: they rule out the treatable physical causes. Sleep, stress, low mood, alcohol and some medicines explain most of what's left. If tiredness lasts more than six weeks and gets worse after activity, ask about ME/CFS, which NICE says can be diagnosed after three months.

Can a home kit replace a GP blood test for tiredness?

Not fully. None of the home kits we checked covers all five tests; most leave out the full blood count or the coeliac screen, and some add vitamin D, which guidelines don't recommend for tiredness. A clinician also checks for red flags and acts on the result. A kit is most useful while you wait for an appointment.

Sources

General information, not medical advice — see our medical disclaimer. Written to the WhereToStart editorial policy. Next scheduled review: 15 April 2027.

Why am I always tired? The five blood tests worth asking for