ARR Screening Calculator
Use this tool to calculate the aldosterone-to-renin ratio (ARR), a common screening metric for possible primary aldosteronism.
What is the aldosterone-to-renin ratio?
The aldosterone-to-renin ratio (ARR) compares how much aldosterone your body is producing relative to renin. It is one of the most useful first-line screening tools for primary aldosteronism (also called Conn syndrome), a condition where excess aldosterone can drive high blood pressure and low potassium.
In simple terms:
- Aldosterone helps regulate sodium and potassium balance.
- Renin is part of the renin-angiotensin-aldosterone system (RAAS) and usually rises or falls to maintain blood pressure and volume.
- When aldosterone is inappropriately high while renin is suppressed, the ARR rises and may signal a clinically important endocrine cause of hypertension.
How this calculator works
Formula used
For both assay types, the calculator divides aldosterone (converted to ng/dL when needed) by renin:
- PRA mode: ARR = aldosterone (ng/dL) ÷ PRA (ng/mL/hr)
- DRC mode: ARR = aldosterone (ng/dL) ÷ DRC (mU/L)
The numeric ARR can look very different depending on the renin method and local lab calibration. Always compare with your laboratory's reference framework.
Why units matter
ARR cutoffs are highly unit-dependent. If you switch from ng/dL to pmol/L for aldosterone, or from PRA to DRC for renin, the threshold for a “positive” screen changes. That is why this calculator shows a method-aware interpretation instead of a one-size-fits-all diagnosis.
How to prepare for ARR testing
Pre-analytic conditions can strongly alter ARR results. Proper preparation improves accuracy and reduces false positives and false negatives.
Typical preparation checklist
- Correct low potassium before testing when possible.
- Maintain a usual (not sodium-restricted) salt intake unless your clinician says otherwise.
- Follow instructions about posture and timing (often morning collection after being upright for a period).
- Review medications in advance with your clinician, especially blood pressure drugs.
Medications that can affect ARR
Many antihypertensive medications can change aldosterone, renin, or both. Examples include:
- Mineralocorticoid receptor antagonists (spironolactone, eplerenone)
- Diuretics
- ACE inhibitors and ARBs
- Beta blockers
- Calcium channel blockers
- Central alpha agonists
Some medications suppress renin and can make ARR appear artificially high, while others raise renin and can lower ARR. Never stop prescription medications on your own—coordinate changes with your healthcare team.
Interpreting ARR results
If PRA is used
A commonly cited screen-positive zone is roughly ARR around 20 to 30 or higher (in ng/dL per ng/mL/hr), typically with aldosterone above a minimum threshold (often around 10 to 15 ng/dL, depending on protocol). Higher values raise suspicion for primary aldosteronism, but do not confirm it.
If DRC is used
DRC-based ARR cutoffs vary more by assay platform and institution. Some centers use lower numeric thresholds than PRA-based systems, and the exact trigger for confirmatory testing is lab-specific. For DRC results, always rely on local reference guidance.
What happens after a positive screen?
A positive ARR is usually followed by confirmatory testing rather than immediate diagnosis. Depending on your care pathway, next steps may include:
- Confirmatory suppression testing
- Adrenal imaging (such as CT)
- Adrenal vein sampling in selected patients
- Treatment planning (medical therapy vs. surgery) based on subtype
Identifying primary aldosteronism matters because targeted treatment can significantly improve blood pressure control and reduce cardiovascular risk.
Limitations of any ARR calculator
- Cannot account for all assay-specific laboratory differences.
- Cannot replace clinical history, physical exam, and medication review.
- Cannot determine confirmatory diagnosis.
- Can be skewed by incomplete preparation or unstable potassium status.
Quick FAQ
Is a high ARR definitive for primary aldosteronism?
No. It is a screening result that usually prompts confirmatory testing.
Can normal potassium rule out primary aldosteronism?
No. Many patients with primary aldosteronism have normal potassium levels.
Should I interpret this calculator alone?
Use it for education and discussion. Final interpretation should come from your clinician and your laboratory method.