EDTA plasma (Purple Top)
Minimum volume: 3 mL
Upright: 103 – 1197 pmol/L
Supine: 103 – 859 pmol/L
ARR >30 pmol/mIU is suggestive of primary hyperaldosteronism (aldosterone is usually >400 pmol/L)
Referral test – within 2 weeks
Sample is unstable and should be sent to laboratory immediately to be separated and frozen.
Unrestricted dietary salt intake day before test
Discontinue anti-hypertensives that may interfere with interpretation of test for at least 4 weeks (e.g. spironolactone, amiloride, K+ wasting diuretics)
Correct any underlying hypokalaemia if possible
Before sample collection, patient should be ambulant for 2 hours and then seated for 5-15 minutes
Aldosterone is a mineralocorticoid produced by the adrenal cortex which acts to maintain blood pressure and extracellular fluid volume. Aldosterone is secreted in response to decreased blood pressure and extracellular fluid volume via activation of the renin-angiotensin-aldosterone pathway. Aldosterone promotes the renal absorption of sodium in exchange for potassium, resulting in retention of water.
Inappropriately high levels of aldosterone can result in hypertension, known as primary hyperaldosteronism (Conn’s syndrome). Therefore, measurement of aldosterone, usually in addition with renin to calculate the aldosterone renin ratio (ARR), is used in the investigation of drug-resistant hypertension to screen for Conn’s syndrome. Further testing, such as a saline suppression test, should be used in the event of a raised ARR to confirm the diagnosis.