Blood Tests for Dizziness and Lightheadedness
Feeling dizzy, faint, or unsteady? A blood test can often reveal exactly why. Here are the markers your GP should check and what each one means.
Types of Dizziness Explained
Not all dizziness is the same. The word “dizzy” actually describes several different sensations, and distinguishing between them helps your doctor know which tests to order. The type of dizziness you experience is the single most important clue to its cause.
Blood tests are most useful for presyncope (feeling faint) and non-specific dizziness. For vertigo (room spinning), the cause is usually in the inner ear rather than the blood, though some blood markers still matter.
Presyncope (Lightheadedness)
Feeling faint, like you are about to pass out. The room does not spin, but you feel unsteady and your vision may grey out.
Common causes: Low blood pressure, anaemia, dehydration, blood sugar drops, heart rhythm issues
Vertigo (Room Spinning)
The room spins around you, or you feel like you are spinning. Often comes with nausea. Triggered by head movements.
Common causes: Inner ear problems (BPPV, labyrinthitis), Meniere's disease, vestibular neuritis
Disequilibrium (Unsteadiness)
Feeling off-balance or unsteady on your feet, especially when walking. No spinning sensation.
Common causes: B12 deficiency (nerve damage), medication side effects, peripheral neuropathy
Non-Specific Dizziness
A vague feeling of being “off” or “swimmy” that is hard to describe. Not spinning, not faint, just not right.
Common causes: Anxiety, thyroid dysfunction, electrolyte imbalances, chronic fatigue
8 Causes of Dizziness Your Blood Can Reveal
These are the conditions that cause dizziness and can be detected or ruled out with standard blood tests. Many are surprisingly common and easily treatable once identified.
Anaemia (Low Haemoglobin)
How it causes dizziness: Haemoglobin carries oxygen in your red blood cells. When levels drop, your brain receives less oxygen — especially when you stand up quickly and blood pools in your legs. Your brain essentially goes into power-saving mode, causing that grey-out, faint feeling.
Pattern to recognise: Worst when standing up quickly. Improves when lying down. Often accompanied by shortness of breath on stairs and a racing heart during mild exertion. Pale inner eyelids are a classic sign.
Iron Deficiency
How it causes dizziness: Iron deficiency can cause dizziness even before you become frankly anaemic. Your ferritin (iron stores) may be critically low while your haemoglobin is still just within range. The brain is exquisitely sensitive to early iron depletion because iron is needed for neurotransmitter production, not just oxygen transport.
Pattern to recognise: Gradual onset over weeks or months. Worse with exercise. Often paired with fatigue, cold hands, brittle nails, and unusual cravings (ice, dirt, cornstarch). Women with heavy periods are at highest risk.
Blood Sugar Dysregulation
How it causes dizziness: Your brain uses about 20% of your body’s glucose despite being only 2% of your weight. When blood sugar drops (hypoglycaemia) or swings wildly (pre-diabetes), the brain is the first organ to protest. Both low and high blood sugar cause dizziness through different mechanisms — low sugar starves the brain, high sugar causes dehydration.
Pattern to recognise: Dizziness 2-4 hours after eating suggests reactive hypoglycaemia. Dizziness with excessive thirst, frequent urination, and blurred vision suggests diabetes. An afternoon “head swim” after a carb-heavy lunch is the most common complaint.
Thyroid Dysfunction
How it causes dizziness: Both underactive and overactive thyroids cause dizziness, but through different pathways. Hypothyroidism causes low blood pressure and slow heart rate, reducing blood flow to the brain. Hyperthyroidism causes a racing heart and palpitations that can make you feel faint. Both also affect the vestibular system directly.
Pattern to recognise: Hypothyroid dizziness: slow and constant, worse in cold weather, with weight gain and fatigue. Hyperthyroid dizziness: sudden episodes with palpitations, tremor, and anxiety. Both can cause positional dizziness.
Electrolyte Imbalances
How it causes dizziness: Electrolytes are the minerals that keep your nerves firing and muscles contracting — including your heart muscle. Low sodium (hyponatraemia) is the single most common electrolyte cause of dizziness in older Australians, often caused by blood pressure medications, excessive water intake, or hot weather.
Pattern to recognise: Low sodium: confusion plus dizziness (especially in over-65s on diuretics). Low potassium: dizziness with muscle cramps and weakness. Low magnesium: dizziness with tremor, twitching, and irregular heartbeat. Often multiple electrolytes are off together.
Vitamin B12 Deficiency
How it causes dizziness: B12 is critical for maintaining the myelin sheath that insulates your nerves. When B12 is low, the vestibular nerve (which controls balance) and peripheral nerves (which tell your brain where your feet are) degrade. This causes a distinctive unsteadiness and “floating” sensation quite different from the lightheadedness of anaemia.
Pattern to recognise: Unsteadiness rather than true faintness. Worse in the dark or with eyes closed (your damaged nerves rely more on vision). Often paired with tingling in hands and feet, memory problems, and a smooth sore tongue. Vegans, vegetarians, and people over 60 are at highest risk.
Dehydration & Kidney Function
How it causes dizziness: Your kidneys regulate blood volume. When kidney function declines or you are chronically dehydrated, blood volume drops and your blood pressure falls — especially on standing. Elevated urea and creatinine alongside concentrated blood (high haematocrit) can reveal chronic mild dehydration that blood pressure readings alone may miss.
Pattern to recognise: Worst on standing up (orthostatic hypotension). Improves after drinking fluids. Dark yellow urine. Chronic mild dehydration is remarkably common in older Australians who deliberately limit fluids to avoid bathroom trips.
Adrenal Insufficiency
How it causes dizziness: Your adrenal glands produce cortisol, which maintains blood pressure and blood sugar. When cortisol is low (Addison’s disease or adrenal fatigue), blood pressure drops, blood sugar falls, and sodium decreases — a triple hit that makes you dizzy, especially in the mornings or during stress.
Pattern to recognise: Worst in the morning. Worsened by stress or illness. Salt cravings are a distinctive clue. Low blood pressure that drops further on standing. Often paired with extreme fatigue, nausea, and darkening skin on knuckles and elbows.
When Does Your Dizziness Happen?
The timing of your dizziness is a powerful diagnostic clue. Match your trigger below to find which blood tests are most likely to reveal the cause.
| When It Happens | Likely Cause | Key Tests | Urgency |
|---|---|---|---|
| Standing up quickly | Anaemia, dehydration, low blood pressure, adrenal insufficiency | FBC, Iron Studies, Electrolytes, Cortisol | Routine GP |
| After eating (30-90 min) | Reactive hypoglycaemia, postprandial hypotension | HbA1c, Fasting Glucose | Routine GP |
| Skipping meals | Hypoglycaemia, poor glucose regulation | Fasting Glucose, HbA1c, Insulin | Routine GP |
| In hot weather | Dehydration, electrolyte loss, heat sensitivity (thyroid) | Electrolytes, eGFR, TSH | Routine GP |
| During or after exercise | Iron deficiency, anaemia, dehydration | Ferritin, FBC, Electrolytes | Routine GP |
| Constant / all day | Thyroid dysfunction, B12 deficiency, chronic anaemia | TSH, B12, FBC, Iron Studies | Routine GP |
| With palpitations | Thyroid (hyper), anaemia, electrolyte imbalance, anxiety | TSH, FBC, Magnesium, Potassium | See GP soon |
| With headache | Anaemia, dehydration, blood pressure, blood sugar | FBC, Electrolytes, Glucose | See GP soon |
| In the morning only | Low cortisol, dehydration, blood sugar drop overnight | Morning Cortisol, Glucose, Electrolytes | Routine GP |
| During period | Iron deficiency from menstrual blood loss | Ferritin, FBC | Routine GP |
The Dizziness Blood Panel
If your GP can order one set of blood tests to investigate dizziness, this panel covers the most common treatable causes. In Australia, nearly all of these tests are bulk billed when clinically indicated.
| Test | What It Checks | Cost (Australia) |
|---|---|---|
| Full Blood Count (FBC) | Haemoglobin, RBC — detects anaemia | Bulk billed |
| Iron Studies (Ferritin, Fe, TIBC) | Iron stores — low ferritin even with normal Hb | Bulk billed |
| Thyroid Function (TSH, Free T4) | Under/overactive thyroid | Bulk billed |
| Electrolytes (Na, K, Cl, HCO3) | Sodium, potassium — nerve and muscle function | Bulk billed |
| Fasting Glucose | Current blood sugar level | Bulk billed |
| HbA1c | 3-month average blood sugar | Bulk billed |
| Vitamin B12 | Nerve function and vestibular health | Bulk billed |
| Kidney Function (eGFR, Creatinine) | Hydration and kidney filtration | Bulk billed |
| Magnesium | Nerve signalling and muscle function | Bulk billed |
| Calcium | Muscle contraction and nerve transmission | Bulk billed |
| Vitamin D (25-OH) | Muscle weakness, balance issues | Bulk billed* |
| Morning Cortisol | Adrenal function (if other tests normal) | Bulk billed |
* Vitamin D is bulk billed when there is a clinical indication such as dizziness, muscle weakness, falls risk, or limited sun exposure. Your GP will know when to order it.
What to Ask Your Doctor
Dizziness is one of those symptoms where how you describe it matters enormously. Use this script when talking to your GP to ensure you get the right tests ordered.
“I've been experiencing dizziness that feels like [faintness / spinning / unsteadiness / general wooziness]. It tends to happen [when I stand up / after eating / during exercise / all the time]. It started about [timeframe] ago and it's [getting worse / staying the same / comes and goes]. I'd like to get blood tests to rule out anaemia, iron deficiency, thyroid issues, blood sugar problems, and electrolyte imbalances. Could we also check my B12 and vitamin D?”
Also mention if applicable:
Any medications you take (especially blood pressure pills, diuretics, or diabetes medication)
Whether you've fainted or nearly fainted
How much water you drink daily (dehydration is underdiagnosed)
Whether the dizziness affects your ability to drive or work
Any recent dietary changes (new vegetarian/vegan diet, dieting, meal skipping)
Red Flags: When Dizziness Needs Emergency Care
Most dizziness is not dangerous — but some combinations of symptoms require immediate attention. Call 000 or go to the emergency department if you experience dizziness with any of these:
Related Guides
Dizziness often overlaps with other symptoms. If you also experience any of these, the related guide may help you narrow down the cause.
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