Dizziness: Types, Causes and How Doctors Diagnose It

Three Types of Dizziness

BPPV: The Most Common Cause

References

Sources cited on this page. PubMed links open the original abstract.

1. Neuhauser HK, von Brevern M, Radtke A, et al. Epidemiology of vestibular vertigo: a neurotologic survey of the general population. Neurology. 2005;65(6):898–904. PMID 16186531 · doi:10.1212/01.wnl.0000175987.07332.2e

Understanding the Causes of Dizziness: Where Blood Tests Help

Dizziness encompasses distinct symptom subtypes – vertigo (a false sense of movement), presyncope (near-fainting), disequilibrium (unsteadiness), and non-specific light-headedness – each with different aetiologies. Blood tests are most informative for the systemic and metabolic causes of dizziness, particularly presyncope and light-headedness, where haematological, endocrine, and cardiovascular abnormalities are frequently identified. True vertigo from inner ear or cerebellar pathology is diagnosed clinically (Dix-Hallpike test, HINTS exam) and on imaging; blood tests play a supporting role.¹

Anaemia is a common and overlooked cause of persistent dizziness, particularly in premenopausal women and those with poor dietary intake. A low haemoglobin reduces oxygen delivery to the vestibular brainstem and cerebellum, producing light-headedness on standing and during exertion. Full blood count is the first test to request. Iron-deficiency anaemia, B12 deficiency, and folate deficiency are the most treatable causes – each identifiable by specific blood markers (ferritin, serum B12, red cell folate) and each correctable with supplementation or treatment of the underlying cause.

Blood Glucose, Thyroid, and Autonomic Dizziness

Hypoglycaemia is an acute and potentially dangerous cause of dizziness, sweating, and confusion – most commonly in people with diabetes on insulin or sulphonylureas. A capillary or venous glucose during a symptomatic episode is diagnostic; HbA1c identifies the background glycaemic control pattern. Postprandial hypoglycaemia – occurring two to four hours after carbohydrate-rich meals in people without diabetes – is under-recognised and produces dizziness that patients often attribute to blood pressure changes. A glucose tolerance test with glucose measurements at 0, 30, 60, 90, and 120 minutes can capture the postprandial nadir.²

Thyroid dysfunction causes dizziness through two distinct mechanisms: hypothyroidism produces bradycardia, hypotension, and low cardiac output (causing presyncope); hyperthyroidism causes tachycardia, increased cardiac output, and palpitations that patients describe as dizziness. Both are identified by serum TSH as the single best screening test. Adrenal insufficiency (low cortisol, high ACTH) causes postural hypotension and dizziness through mineralocorticoid deficiency and volume depletion – a morning serum cortisol below 100 nmol/L is strongly suggestive and warrants formal short synacthen testing.

Cardiovascular and Medication-Related Dizziness

Postural (orthostatic) hypotension – a fall in systolic blood pressure of ≥20 mmHg or diastolic ≥10 mmHg within three minutes of standing – is a common cause of dizziness in older adults and those on antihypertensives, diuretics, or alpha-blockers. Blood tests in this context look for contributing factors: electrolytes and renal function (diuretic-induced hypokalaemia or hyponatraemia), full blood count (anaemia amplifying the haemodynamic effect), and where autoimmune dysautonomia is suspected, ANA and anti-Ro/La antibodies. BNP or NT-proBNP is measured when cardiac dysfunction contributes, as even mild left ventricular impairment can cause exertional dizziness through reduced stroke volume reserve.³

Getting the description right is most of the diagnosis

Dizziness is one of those complaints where the words matter more than any test. A spinning sensation, where the room appears to move, is vertigo and points to the inner ear or, less often, the brainstem. A sense of impending faint, greying vision and clamminess is presyncope and points to blood pressure, heart rhythm or volume. Unsteadiness only on standing and walking, with no spinning, points towards balance and proprioception, common with age, neuropathy or medication. Vague lightheadedness without any of these features is the least specific and is frequently related to anxiety, hyperventilation or medication.

Medication is one of the commonest reversible causes

• Blood pressure medicines, especially after a dose increase or in hot weather when fluid loss is higher.
• Diuretics, which can cause both volume depletion and low sodium or potassium.
• Alpha blockers such as tamsulosin, a well-known cause of postural drops.
• Sedatives, opioids and some antidepressants, particularly in older adults and in combination.
• Gentamicin and related antibiotics, which can damage the balance organ directly.

Warning features that point away from the inner ear

Most vertigo is peripheral and benign, but a few features suggest a central cause needing urgent imaging: new severe headache or neck pain, double vision, slurred speech, facial or limb weakness or numbness, difficulty swallowing, or an inability to walk unaided even when sitting still feels tolerable. Vertigo that begins suddenly in someone with vascular risk factors, or that is accompanied by any new neurological sign, should be assessed the same day rather than treated as an ear problem.

Practical measures while the cause is sorted out

If symptoms are postural, rising in stages rather than all at once, sitting on the edge of the bed before standing, and maintaining fluid and salt intake where that is appropriate all help. Compression stockings assist some people. For confirmed benign positional vertigo, repositioning manoeuvres performed by a trained clinician are considerably more effective than medication, and vestibular sedatives such as prochlorperazine are best used briefly, as prolonged use delays the natural compensation that resolves symptoms.