Lab Tests Online
Deliver to lab within 6 hr of sample collection. Correct hypokalaemia before taking the sample.
Effect of drugs
Ideally, Spironolactone, which inhibits aldosterone formation, must be stopped six weeks before testing. The test is fairly robust with other drugs but
the aldosterone/renin ratio may sometimes be altered by:
- loop diuretics & calcium antagonists (false high ratio)
- ß-blockers, NSAIDs & methyl dopa (false low ratio)
- ACE inhibitors lower the aldosterone/renin ratio in normal patients, but in patients with Conn’s syndrome, the ratio usually remains high.
The basic pathology is an adrenal adenoma (2/3) or adrenal hyperplasia (1/3) causing:
- hypokalaemia, with serum potassium classically <3.5 mmol/L but often in the range 3.5-3.9 mmol/L with an elevated aldosterone/renin ratio. This is the most sensitive test.
- A positive screening test is an aldosterone/renin ratio >25 (usually >40).
- Typically the renin is suppressed to <15 mU/L and the plasma aldosterone is >220 ng/L (Supine)
- Renin suppression by beta-blockers or NSAIDs may give a false positive screening test.
- A negative screening test is a ratio <25, especially if the renin is >25 mU/L. A negative test is valid in patients who continue taking diuretics, ACE inhibitors or calcium-channel blockers.
This is found in oedematous and hypertensive states where the plasma aldosterone increase is secondary to an increased renin, e.g. diuretic therapy or renal artery stenosis.
Cannot be added to existing request
Specimen Labelling Procedure