Aldosterone-Renin Ratio (ARR) Calculator
Aldosterone-Renin Ratio (ARR) Calculator
Screen for primary aldosteronism from plasma aldosterone and plasma renin activity, and see why the ratio is unreliable without checking the aldosterone alongside it.
Aldosterone-Renin Ratio (ARR)
Aldosterone ÷ reninPlasma aldosterone 22 ng/dL, plasma renin activity 0.4 ng/mL/hr
Formula
- aldosterone
- ng/dL
- PRA
- plasma renin activity, ng/mL/hr
- screening threshold
- commonly an ARR above 30 together with an aldosterone above 15 ng/dL — the ratio alone, without the absolute aldosterone, is misleading
Worked example
Plasma aldosterone 22 ng/dL, plasma renin activity 0.4 ng/mL/hr
22 ÷ 0.4 = 55.0
Above 30, with aldosterone above 15 ng/dL → suggestive of primary aldosteronism
Drugs that interfere with the ratio
| Drug class | Effect | Action before testing |
|---|---|---|
| Spironolactone, eplerenone | Stop the test working entirely | Withhold for 4 – 6 weeks |
| Beta-blockers, clonidine | Suppress renin — false positive | Withhold where feasible before testing |
| ACE inhibitors, ARBs | Raise renin — false negative | Withhold where feasible before testing |
| Diuretics | Raise renin — false negative | Withhold where feasible before testing |
What the ratio screens for, and where it misleads
The aldosterone-renin ratio screens for primary aldosteronism, the commonest identifiable and potentially curable cause of hypertension. A commonly used screening cut-off is an ARR above 30, measured in ng/dL per ng/mL/hr, together with an aldosterone above 15 ng/dL. The second condition matters as much as the first: the ratio alone is misleading when renin is very suppressed, because dividing by a tiny denominator inflates the ratio regardless of whether aldosterone is genuinely raised. A high ratio with a low-normal aldosterone is not a positive screen.
Interfering drugs have to be addressed before the sample is drawn. Spironolactone and eplerenone act directly on the pathway being tested and stop it working, so both need withholding for four to six weeks. Beta-blockers and clonidine suppress renin and produce a false-positive ratio; ACE inhibitors, angiotensin receptor blockers and diuretics raise renin and produce a false-negative one. Hypokalaemia should be corrected before testing rather than around it, since potassium is a direct secretagogue for aldosterone and hypokalaemia suppresses secretion, which can mask genuine primary aldosteronism.
The sample itself should be drawn seated, mid-morning, after the patient has been upright for about two hours — posture and the time of day both move the result. A positive screen is not a diagnosis: it needs a confirmatory suppression test, and adrenal vein sampling before any decision about surgery.
Frequently asked questions
What ARR indicates primary aldosteronism?
Commonly an ARR above 30, with aldosterone and renin in ng/dL and ng/mL/hr, together with an absolute aldosterone above 15 ng/dL. The ratio alone, without checking the aldosterone, is not enough.
Why can a suppressed renin give a false-positive ratio?
Dividing by a very small renin inflates the ratio even when aldosterone is not truly raised. This is why the aldosterone must always be checked in absolute terms alongside the ratio, not the ratio alone.
Which drugs must be stopped before testing?
Spironolactone and eplerenone act directly on the pathway and must be withheld for 4 to 6 weeks. Beta-blockers and clonidine raise the ratio; ACE inhibitors, ARBs and diuretics lower it — withhold where clinically feasible.
What happens after a positive screen?
A confirmatory suppression test — saline infusion, fludrocortisone suppression or a captopril challenge — is required, followed by adrenal vein sampling before any decision about surgery.
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References
- Funder JW et al. The management of primary aldosteronism: case detection, diagnosis, and treatment. Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. 2016;101(5):1889–916.
- Young WF Jr. Primary aldosteronism: renaissance of a syndrome. Clin Endocrinol. 2007;66(5):607–18.