Renin

The range applies to direct renin concentration in an upright person (lying values are lower, roughly 3 to 40 mU/L), and some labs instead report plasma renin activity in ng/mL/h or pmol/L/h, which is a different measurement with its own range and cannot be converted.

Renin is an enzyme released by the kidneys when they sense low blood pressure, low salt or reduced blood flow. It sets off a chain of reactions that ends with aldosterone and with narrowing of blood vessels, raising blood pressure. Most UK laboratories now measure the amount of renin directly, though some older or overseas reports measure its activity instead.

It is requested with aldosterone when high blood pressure is difficult to control, starts young or comes with low potassium, to look for primary aldosteronism, in which renin is suppressed. It is also used in adrenal failure, in monitoring treatment of some adrenal conditions, and when unusual salt and potassium results are being looked into.

• Standing up, being short of fluid, a low-salt diet and diuretic (water) tablets
• Many blood pressure tablets, especially ACE inhibitors, ARBs and some others
• Kidney artery narrowing and some kidney diseases
• Adrenal failure (Addison's disease)
• Heart failure and liver cirrhosis
• Pregnancy and the second half of the cycle

• Primary aldosteronism, where aldosterone is high and switches renin off
• A high-salt diet, lying flat and fluid overload
• Beta-blockers, some anti-inflammatory painkillers and some other blood pressure tablets
• Older age and Black African or Caribbean ancestry, in the general population
• Liquorice and some steroid medicines
• Some rare inherited conditions

• Posture, salt intake, fluid intake and time of day change it several-fold
• Almost every blood pressure tablet moves it, so doctors usually adjust medicines for a few weeks before the test
• A sample left in the fridge or on ice before separation can read falsely high
• Direct renin and renin activity are different measurements with different units and ranges

Taken with aldosterone, in the morning after being up for two hours, on a normal-salt diet, usually after certain blood pressure tablets have been paused under medical supervision. The tube is kept at room temperature, not on ice. Posture and medicines should be recorded.

Written by a UK consultant physician. Typical UK adult reference ranges; your laboratory's own printed range takes precedence.