Special Precautions/Comments:

Sample is unstable and should be sent to laboratory immediately to be separated and frozen.

Patient preparation:

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

Additional Information:

Renin is synthesised and secreted by juxtaglomerular cells in the kidney in response to low blood pressure and extracellular fluid volume. Renin acts to restore blood pressure and extracellular fluid volume by stimulating secretion of aldosterone via 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 renin and aldosterone can result in hypertension, known as primary hyperaldosteronism (Conn’s syndrome). Therefore, measurement of renin, usually in addition with aldosterone 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. Measurement of renin can also be used to assess mineralocorticoid replacement in adrenal insufficiency (Addison’s disease) or congenital adrenal hyperplasia (CAH). 

Assays for renin concentration (mass) or renin activity are available.