Symptom · Dizziness and light-headedness
"Dizzy" describes two completely different experiences, and which one you have decides whether a blood test is the right tool. If the room spins, that is vertigo, and it is nearly always the inner ear or the balance nerves. No blood test sees it, and the answer is an examination and often a simple repositioning manoeuvre that works in minutes. If instead you feel faint, woozy, unsteady, worse on standing, worse when you have not eaten, then the cause is usually in the blood or the blood pressure, and that is measurable: anaemia and low iron, blood sugar, thyroid, B12, electrolytes, kidney function, cortisol and, occasionally, coeliac disease.
Venous draw at 103 UK clinics or at home. Report within 48 hours of the lab receiving your sample. No GP referral.
Last reviewed 17 September 2026
The short answer
A blood test for dizziness should cover a full blood count with ferritin and iron studies, HbA1c and fasting glucose, a full thyroid panel, B12 and folate, sodium, potassium, calcium and magnesium, kidney function with cystatin C, and morning cortisol. It is the right first step for light-headedness, faintness and unsteadiness. It is the wrong tool for true spinning vertigo, which needs an examination, and it is no use at all in an emergency.
Call 999 now, do not book a test, if dizziness comes with
Weakness or numbness on one side, drooping face, slurred or muddled speech, sudden severe headache, double vision or loss of vision, chest pain, or a first fainting episode with no warning. These can be signs of stroke or a heart problem and are time-critical. Also see a GP urgently, within days, for dizziness with new deafness or ringing in one ear, dizziness after a head injury, repeated falls, or black or bloody stools alongside light-headedness, which suggests active bleeding.
First, which kind
Vertigo · not a blood test
A definite sense of spinning or tilting, often triggered by rolling over in bed, looking up or turning your head, lasting seconds to minutes, sometimes with nausea. This is usually benign paroxysmal positional vertigo, or vestibular neuritis after a virus, or Meniere's if it comes with hearing changes. A GP or physiotherapist can diagnose it by examining your eye movements, and BPPV is often fixed in one appointment with the Epley manoeuvre. Blood tests are normal in all of these, so the panel is not the place to start. If this describes you, book the GP, not the test.
Light-headed · measurable
Woozy, swimmy, unsteady, grey at the edges. Worse standing up quickly, worse in a hot shower, worse if you have skipped a meal, often with tiredness, breathlessness on stairs or palpitations. This is the picture of anaemia, low iron, unstable blood sugar, a thyroid problem, dehydration or low blood pressure, and it is exactly what a blood panel is for.
A third group is neither: persistent dizziness with anxiety, screen use and busy environments, sometimes called persistent postural-perceptual dizziness. It is real, common after a vertigo episode, and treated with vestibular rehabilitation rather than tablets or tests. A clean blood panel is part of getting to that diagnosis.
What to test
| Marker | How it makes you dizzy | What to look for | Panel |
|---|---|---|---|
| Full blood count and ferritin | Anaemia means less oxygen reaching the brain: light-headedness on standing or exertion, with breathlessness, pallor and fatigue. Low iron without anaemia does it too, more mildly | Haemoglobin below 120 g/L in women or 130 in men; ferritin below 30; small pale red cells | All panels |
| HbA1c and fasting glucose | Blood sugar dips cause shakiness, sweating and light-headedness that settle after eating. Most important if you take insulin or a sulfonylurea, where it can be dangerous | HbA1c above 48 (diabetes) or a low fasting glucose; symptoms clearly linked to meals | All panels; fasting insulin in Ultimate and Signature |
| Thyroid (TSH, free T4, free T3) | Overactive causes palpitations, tremor and faintness; underactive causes a slow pulse, low blood pressure and unsteadiness | TSH outside range in either direction; free T4 or T3 abnormal | All panels |
| Vitamin B12 and folate | B12 deficiency damages the nerves that carry position sense from your feet, so you feel unsteady rather than spinning, worse in the dark or with eyes closed. Often with pins and needles | B12 below 300 pmol/L with symptoms; low folate | All panels |
| Sodium, potassium, calcium, magnesium | Low sodium causes confusion and unsteadiness; potassium and magnesium disturbances cause palpitations and faintness; low calcium causes tingling and light-headedness. Common on diuretics, PPIs and after vomiting or heavy sweating | Any result outside range, particularly sodium below 130 mmol/L, which needs prompt medical review | All panels |
| Kidney function (urea, creatinine, eGFR, cystatin C) | Dehydration and impaired kidney function both cause postural light-headedness; a raised urea with a normal creatinine is the classic dehydration pattern | Raised urea relative to creatinine; falling eGFR; cystatin C giving a truer reading in older or slimmer people | Kidney in all; cystatin C in Ultimate and Signature |
| Morning cortisol | Adrenal insufficiency is rare but important: low blood pressure, faintness on standing, salt craving, weight loss, darkened skin and exhaustion. A low morning cortisol is the signal to investigate further | Morning cortisol low (drawn 8 to 9am); low sodium with a high potassium alongside makes it more likely | All panels |
| Coeliac screen (tTG-IgA) | Undiagnosed coeliac disease causes iron, B12 and folate deficiency together, which is why the dizziness does not resolve with supplements alone | Positive tTG while still eating gluten | Signature digestive profile |
Thresholds are UK laboratory conventions and NICE guidance where it exists. Your report reads each result against the others. Guides: ferritin and iron studies, HbA1c, thyroid, B12, kidney and cystatin C, cortisol.
Read it in context
Pattern 1
Ferritin under 15, haemoglobin at or below the bottom of range, small pale cells. Iron deficiency anaemia, and in a woman under 50 the cause is usually heavy periods, in anyone else it is a reason to look for bleeding from the gut. Both need addressing, not just the iron. Heavy periods and iron.
Pattern 2
B12 low or borderline, sometimes with a raised MCV. This is a nerve problem rather than a blood pressure one, and it is worth treating promptly because prolonged deficiency can cause lasting damage. Homocysteine in the Signature panel confirms it when B12 is in the grey zone.
Pattern 3
Common, and genuinely useful. It rules out anaemia, thyroid, electrolytes and diabetes, which is what a GP would want excluded, and points to the causes blood cannot see: inner-ear vertigo, low blood pressure on standing, medication side effects, dehydration, anxiety or vestibular migraine. Take the clean panel to your GP and the conversation starts further along.
Which panel
Enough for most
Advanced
74 biomarkers · £269
Full blood count, ferritin with iron studies, HbA1c and glucose, full thyroid with antibodies, B12, folate, sodium, potassium, calcium, magnesium, kidney, liver and morning cortisol. Seven of the eight causes in the table.
View AdvancedUltimate
114 biomarkers · £349
Adds cystatin C for a truer kidney reading, fasting insulin and HOMA-IR for blood sugar swings, and the complete hormone set. Worth it if you are over 50, on several medications, or the dizziness comes with weight change.
View UltimateSignature
230 biomarkers · £799
Processed by Randox. Adds homocysteine, which confirms a functional B12 deficiency when the level is borderline, and the digestive profile including coeliac screening.
View SignatureClinic draw £19. At-home £39, which is the sensible option if standing up makes you faint. Morning slot, fasted from 10pm. Keep eating gluten before a coeliac screen. Pay monthly available.
Honest comparison
Most of the common causes of dizziness, if we are being straight about it. Inner-ear vertigo, which is the single biggest group, is invisible to blood and diagnosed by watching your eyes as your head is moved. Orthostatic hypotension, a blood pressure that drops when you stand, needs a cuff and two readings, not a tube. Vestibular migraine, anxiety-driven dizziness and persistent postural-perceptual dizziness are all clinical diagnoses. And medication is a huge cause that no panel reveals: blood pressure tablets, diuretics, antidepressants, sedatives, alpha blockers and anything new started in the last month. The reason to test anyway is that the treatable blood causes are serious when present and easily missed, and the pattern of symptoms does not reliably tell them apart from the rest. If your dizziness is spinning, or you are on several medications, start with your GP. If it is faintness, tiredness and unsteadiness, start with the blood. What to ask your GP for.
After your result
Anaemia, iron, blood sugar, thyroid, B12, electrolytes, kidney or cortisol, each read against the others, with anything needing prompt medical attention flagged clearly. Reviewed by a medical professional before it reaches you.
A low sodium, a low morning cortisol, a new anaemia or a thyroid result all need a doctor, and some need one quickly. Iron and B12 you can start correcting while you wait. The report tells you which is which.
A clean panel moves the conversation to blood pressure, the inner ear, your medication list and vestibular rehabilitation, which is where the answer usually is. That is progress, not a wasted test.
FAQs
A full blood count with ferritin and iron studies, HbA1c and fasting glucose, a full thyroid panel, B12 and folate, sodium, potassium, calcium and magnesium, kidney function, and morning cortisol. Those cover the measurable causes of light-headedness.
Not usually. True spinning vertigo is nearly always an inner-ear or balance-nerve problem, and blood tests are normal. It is diagnosed by examination, and the commonest form, BPPV, is often treated in a single appointment with a repositioning manoeuvre. A blood test is useful for excluding other causes, not for finding vertigo.
Yes. Anaemia reduces oxygen delivery and causes light-headedness on standing or exertion, along with breathlessness and fatigue. Low ferritin without full anaemia causes a milder version. In women under 50 the usual cause is heavy periods; in men and postmenopausal women, new iron deficiency should prompt a GP conversation about bleeding from the gut.
Yes, and it feels different: unsteadiness rather than spinning, worse in the dark or with eyes closed, often with pins and needles in the hands or feet. It is worth treating promptly, because long-standing deficiency can cause lasting nerve damage.
Call 999 if it comes with weakness or numbness on one side, facial drooping, slurred speech, sudden severe headache, double vision, chest pain, or fainting without warning. Those can indicate stroke or a cardiac cause. Seek same-week GP review for dizziness with new one-sided hearing loss, after a head injury, or with black or bloody stools.
That is a useful result. It points to the causes blood cannot show: inner-ear vertigo, a blood pressure that falls on standing, vestibular migraine, medication side effects, dehydration or anxiety-related dizziness. Take the panel to your GP; with the blood causes excluded, the next steps are a lying and standing blood pressure, a medication review and often vestibular rehabilitation.
Yes, and it is the sensible choice if standing or travelling makes you feel faint. A registered phlebotomist visits for £39 and takes the same venous sample a clinic would. How at-home testing works.
Eight measurable causes of light-headedness in one venous draw, at a clinic or at home, with a report within 48 hours that says which it is and what needs a doctor.
Always tired · Heavy periods · Brain fog · Ferritin · Find a clinic
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