Aldosterone to renin ratio (ARR)

The cut-off depends entirely on the units used for each half of the ratio and on the assay (UK labs using direct renin commonly print below 91, below 70 or below 35, while labs using renin activity and ng/dL print figures such as below 30), so only the lab's printed cut-off applies.

The aldosterone to renin ratio is a calculation the laboratory makes by dividing the aldosterone level by the renin level from the same sample. When the adrenal glands make aldosterone on their own, without being told to by renin, aldosterone is high and renin is low, and the ratio climbs. It is the standard first test for the adrenal cause of high blood pressure called primary aldosteronism.

Doctors request it in people whose blood pressure is difficult to control, started young, comes with low potassium or an adrenal nodule on a scan, or runs in the family with early strokes. A raised ratio leads to confirmatory tests in a specialist clinic rather than standing on its own.

• Primary aldosteronism
• Beta-blockers and some other blood pressure tablets, which lower renin
• A high-salt diet
• Older age and Black African or Caribbean ancestry, in the general population, through lower renin
• Kidney disease, in which renin can be low
• The combined contraceptive pill in some women

• Diuretic (water) tablets, ACE inhibitors, ARBs and other medicines that raise renin
• A low-salt diet, being short of fluid and being upright
• Low potassium, which holds aldosterone down
• Pregnancy

• Blood pressure tablets are the commonest reason for a misleading ratio in either direction, which is why medicines are often changed before the test
• Low potassium, salt intake, posture and time of day all shift it
• Very low renin values make the ratio look high even when aldosterone is unremarkable, so doctors read the aldosterone alongside it

It comes from the same morning, upright, normal-salt sample as aldosterone and renin, ideally with potassium in range and after certain blood pressure tablets have been paused under medical supervision. A single raised ratio is repeated or followed by a confirmatory test.

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