What is a positive ARR?

A widely used Endocrine Society cut-off is an ARR above 30 pmol/L per mU/L, combined with an aldosterone that is meaningfully elevated, typically at least about 270 pmol/L or 10 ng/dL. Both conditions reduce false positives from suppressed renin alone.

What is the difference between PRA and direct renin?

Plasma renin activity (PRA) measures the rate of angiotensin generation in ng/mL/h, while direct renin concentration (DRC) measures renin mass in mU/L. The tool converts PRA to DRC using roughly 8.2 mU/L per ng/mL/h so the ratio uses consistent units.

Why must aldosterone also be elevated?

When renin is strongly suppressed for other reasons, the ratio can rise even with a normal or low aldosterone. Requiring an aldosterone above a minimum threshold alongside a high ratio makes the screen more specific for true primary aldosteronism.

What can distort the ARR?

Posture, time of sampling, potassium level, and many drugs affect the result. Beta-blockers raise the ratio, while ACE inhibitors, ARBs, diuretics, and mineralocorticoid receptor antagonists lower it. Sampling conditions should be standardised before interpreting the ratio.

Does a positive screen confirm the diagnosis?

No. A positive ARR is a screening result that should be followed by a confirmatory suppression test such as saline infusion or oral salt loading, then subtype testing. Always interpret against your own laboratory's assay and reference.

What is the Aldosterone-to-Renin Ratio (ARR) Calculator?

Compute the aldosterone-to-renin ratio (ARR) from plasma aldosterone and renin, with unit conversion between pmol/L, ng/dL, direct renin concentration, and plasma renin activity, against the Endocrine Society positive-screen cut-off. It runs free in your browser on Gera Tools, with nothing uploaded.

Aldosterone-to-Renin Ratio (ARR) Calculator

Name: Aldosterone-to-Renin Ratio (ARR) Calculator
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

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The aldosterone-to-renin ratio is the first-line screen for primary aldosteronism, the most common treatable cause of secondary hypertension. This calculator handles the unit conversions that trip people up — aldosterone in pmol/L or ng/dL, renin as activity or concentration — and applies a standard positive-screen rule.

How it works

The ratio is aldosterone divided by renin in consistent units:

aldosterone_pmol = aldosterone_ngdl × 27.7         (if entered in ng/dL)
renin_mU         = PRA_ng_mL_h × 8.2               (if entered as activity)
ARR              = aldosterone_pmol / renin_mU      (pmol/L per mU/L)

A screen is flagged positive when the ARR exceeds 30 pmol/L per mU/L and the aldosterone is at least about 270 pmol/L (10 ng/dL). The aldosterone floor prevents a falsely high ratio when renin alone is suppressed.

Why both thresholds matter

Consider a patient whose renin is strongly suppressed from dehydration or beta-blocker use alone, without any real aldosterone excess. Their aldosterone might be 200 pmol/L — normal or even low — but because renin is near zero, dividing gives an enormous ratio. Requiring the aldosterone to also be meaningfully elevated (the 270 pmol/L floor) catches this situation and prevents a false positive. The two-threshold rule reflects the Endocrine Society guideline that both conditions should coexist for a screen to be considered positive.

Drug effects on the ARR

Many antihypertensive medications alter aldosterone or renin and can shift the ARR significantly in either direction. A brief summary of the main effects:

Drug class	Effect on renin	Effect on aldosterone	Net effect on ARR
Beta-blockers	Suppress	Moderate decrease	Raise ARR — false positives
ACE inhibitors / ARBs	Raise	Lower	Lower ARR — false negatives
Diuretics	Raise	Lower	Lower ARR — false negatives
Calcium channel blockers	Minimal	Minimal	Generally acceptable
Spironolactone / eplerenone	Raise	Lower	Lower ARR — must stop before testing

Ideally, interfering drugs should be washed out for an appropriate period before sampling. Where stopping antihypertensives is unsafe, repeat the test after switching to a medication with minimal ARR effect (such as verapamil or doxazosin) and flag the result as measured on treatment.

What comes after a positive screen

A positive ARR is a screening result only. Before a diagnosis of primary aldosteronism is made, a confirmatory suppression test is needed — typically a four-hour saline infusion or a three-day oral salt loading protocol. If aldosterone fails to suppress below a defined threshold on that test, the diagnosis is confirmed. Subtype testing (adrenal CT, and usually adrenal vein sampling to distinguish a unilateral adenoma from bilateral hyperplasia) then guides whether surgery or medical therapy is the right path.

Notes and limits

ARR cut-offs are strongly assay- and unit-dependent, so always compare against your own laboratory’s reference range. The ratio is also sensitive to posture (seated vs. upright), time of sampling (morning preferred), and potassium level (hypokalemia suppresses aldosterone). This tool is an educational reference only and should not be used for clinical decision-making without specialist oversight.