Calculate the ARR to screen for Primary Aldosteronism
Conventional Units (ng/dL & ng/mL/hr)
SI Units (pmol/L & mU/L)
Unit: ng/dL
Unit: ng/mL/hr
0.00
Medical Disclaimer: This calculator is for educational and screening estimation purposes only. It is not a diagnostic tool. Results vary by laboratory assay methods. Always consult a healthcare professional for diagnosis and interpretation.
function updateLabels() {
var system = document.getElementById('unitSystem').value;
var pacLabel = document.getElementById('pacLabel');
var reninLabel = document.getElementById('reninLabel');
var pacUnit = document.getElementById('pacUnit');
var reninUnit = document.getElementById('reninUnit');
var pacInput = document.getElementById('pacInput');
var reninInput = document.getElementById('reninInput');
if (system === 'conventional') {
pacLabel.innerText = "Plasma Aldosterone Concentration (PAC)";
pacUnit.innerText = "Unit: ng/dL";
reninLabel.innerText = "Plasma Renin Activity (PRA)";
reninUnit.innerText = "Unit: ng/mL/hr";
pacInput.placeholder = "e.g., 25";
reninInput.placeholder = "e.g., 0.5";
} else {
pacLabel.innerText = "Plasma Aldosterone Concentration (PAC)";
pacUnit.innerText = "Unit: pmol/L";
reninLabel.innerText = "Direct Renin Concentration (DRC)";
reninUnit.innerText = "Unit: mU/L";
pacInput.placeholder = "e.g., 550";
reninInput.placeholder = "e.g., 10";
}
// Hide previous results when switching units
document.getElementById('result-container').style.display = 'none';
}
function calculateARR() {
var pac = parseFloat(document.getElementById('pacInput').value);
var renin = parseFloat(document.getElementById('reninInput').value);
var system = document.getElementById('unitSystem').value;
var resultDisplay = document.getElementById('arrResult');
var interpDisplay = document.getElementById('arrInterpretation');
var container = document.getElementById('result-container');
if (isNaN(pac) || isNaN(renin)) {
alert("Please enter valid numeric values for both Aldosterone and Renin.");
return;
}
if (renin === 0) {
alert("Renin value cannot be zero as it would result in an undefined ratio.");
return;
}
var ratio = pac / renin;
// Formatting the result
var formattedRatio = ratio.toFixed(2);
var message = "";
if (system === 'conventional') {
// Logic for ng/dL / ng/mL/hr
// General cutoff is often cited around 20-30 depending on the lab
if (ratio >= 30) {
message = "This ratio is highly suggestive of Primary Aldosteronism (Conn's Syndrome). A confirmatory test is usually recommended.";
} else if (ratio >= 20) {
message = "This ratio is elevated/indeterminate. It may suggest Primary Aldosteronism depending on the specific laboratory cutoff (often >20 or >30) and if PAC > 15 ng/dL.";
} else {
message = "This ratio is within the normal range (<20), making Primary Aldosteronism less likely.";
}
resultDisplay.innerHTML = formattedRatio + " (ng/dL) / (ng/mL/hr)";
} else {
// Logic for SI: pmol/L / mU/L
// Cutoffs vary significantly for DRC, but often cited roughly around 3.7 to 5.7 (ratio * 10 or similar depending on exact unit conversion)
// Common conversion:
// If using pmol/L for PAC and mU/L for DRC.
// A common cutoff for ARR (pmol/L / mU/L) is approximately > 30 to 50 depending on assay.
// *Note: ARR cutoffs are highly assay specific.
// For general pmol/L / mU/L:
// Ratios > 91 (pmol/mU) sometimes used, or simpler ratios.
// Let's use a generic explanatory message acknowledging range variability.
message = "Interpretation of ARR using Direct Renin (SI units) varies heavily by assay manufacturer. Consult your lab's specific reference range.";
// Adding a general guide based on common literature (e.g. Endocrine Society)
// Often if PAC (pmol/L) / DRC (mU/L) > 30-50 it flags attention, but we must be careful.
// Let's stick to the calculation output.
message += "Note: Ensure your Renin unit is mU/L (equivalent to ng/L).";
resultDisplay.innerHTML = formattedRatio + " (pmol/L) / (mU/L)";
}
interpDisplay.innerHTML = message;
container.style.display = 'block';
}
Understanding the Aldosterone-Renin Ratio (ARR)
The Aldosterone-Renin Ratio (ARR) is the most reliable screening test available for detecting Primary Aldosteronism (also known as Conn's syndrome). This condition involves the adrenal glands producing too much of the hormone aldosterone, which can lead to high blood pressure (hypertension) and low potassium levels.
How the Ratio Works
Under normal physiological conditions, renin and aldosterone work together to regulate blood pressure:
Renin: An enzyme released by the kidneys when blood pressure is low.
Aldosterone: A hormone released by the adrenal glands that signals the kidneys to retain salt and water, raising blood pressure.
Usually, if aldosterone is high, renin should be low (suppressed) due to feedback loops. However, in Primary Aldosteronism, aldosterone remains inappropriately high relative to the suppressed renin. Calculating the ratio between these two helps identify this discrepancy.
Plasma Renin Activity (PRA): Measures the capacity of renin to generate angiotensin I. Common in the US. Standard units are ng/mL/hr.
Direct Renin Concentration (DRC): Measures the actual amount of renin protein. Common in Europe and modern automated labs. Standard units are mU/L or ng/L.
Interpretation of Results
Interpretation depends heavily on the units used and the specific assay of the laboratory. Below are general guidelines for Conventional Units (PAC in ng/dL and PRA in ng/mL/hr):
ARR Value (Conventional)
Interpretation
< 20
Normal. Primary Aldosteronism is unlikely.
20 – 30
Indeterminate. Results are borderline. Physicians may look at the absolute PAC level (usually must be >10-15 ng/dL) to decide on further testing.
> 30
Positive Screen. Highly suggestive of Primary Aldosteronism. Confirmatory testing (like a salt loading test) is typically required.
Important Considerations for Accurate Testing
The ARR test is highly sensitive to external factors. To ensure an accurate result, the following preparations are often required (under doctor supervision):
Medications: Spironolactone, Eplerenone, and certain diuretics can significantly alter results and may need to be paused for 4-6 weeks. Beta-blockers and ACE inhibitors also affect renin levels.
Potassium Levels: Hypokalemia (low potassium) suppresses aldosterone. Potassium should be corrected before testing.
Diet: Unrestricted salt intake is recommended prior to the test.
Posture: Blood is usually drawn mid-morning after the patient has been up (ambulatory) for at least 2 hours.
FAQ: Aldosterone Renin Ratio
What is a normal Renin level?
Normal ranges vary by lab, but for Plasma Renin Activity (PRA), a typical normal range for a person on a normal salt diet is roughly 0.6 to 4.3 ng/mL/hr. In Primary Aldosteronism, Renin is usually suppressed to < 1.0 ng/mL/hr or even undetectable.
Can I use this calculator for Direct Renin Concentration?
Yes, select "SI Units" in the dropdown. Note that cutoffs for Direct Renin (DRC) are different than PRA. Because DRC assays vary by manufacturer (e.g., LIAISON vs. IDS-iSYS), there is no single universal cutoff, though ratios are often calculated. Always rely on your lab's reference range.
Why is my ratio high but my doctor says it's normal?
If your Renin is extremely low (e.g., 0.1), the math might produce a very high ratio even if Aldosterone is low. To avoid false positives, doctors also require the Aldosterone level itself to be elevated (usually > 10 or 15 ng/dL) before considering a high ratio significant.