How to Calculate Aldosterone to Renin Ratio
The aldosterone to renin ratio (ARR) is calculated by dividing the plasma aldosterone concentration (measured in ng/dL) by the plasma renin activity (measured in ng/mL/h), with a cutoff value of 30 being commonly used for screening primary aldosteronism. 1, 2
Formula and Units
- ARR = Plasma Aldosterone Concentration (ng/dL) ÷ Plasma Renin Activity (ng/mL/h) 1
- The standard cutoff value is ≥30 when using these units 1, 2
- For a positive test, plasma aldosterone concentration should be at least 10 ng/dL in addition to the elevated ratio 1, 3
Important Considerations for Accurate Measurement
- Patients should be potassium-replete before testing, as hypokalemia can suppress aldosterone production 3
- Blood should be collected in the morning, with the patient seated for 5-15 minutes immediately before collection 3
- Patients should have unrestricted salt intake and normal serum potassium levels 1
- Mineralocorticoid receptor antagonists (spironolactone, eplerenone) should be withdrawn at least 4 weeks before testing 1, 2
- When possible, beta-blockers, centrally acting drugs, and diuretics should be stopped as they can interfere with results 3
- Long-acting calcium channel blockers and alpha-receptor antagonists can be used as alternatives as they minimally interfere with ARR 3
Alternative Calculation Methods
- Some laboratories now measure direct renin concentration (DRC) instead of plasma renin activity 4, 5
- When using direct renin concentration, the formula becomes:
Interpretation Pitfalls
- Low renin can artificially elevate the ARR even without truly elevated aldosterone levels 2
- The specificity of the ratio improves if a minimum plasma renin activity of 0.5 ng/mL/h is used in calculations 2, 3
- A positive screening test requires confirmation with additional testing, such as oral sodium loading with 24-hour urine aldosterone measurement or saline suppression test 3
- Not all patients with primary aldosteronism present with hypokalemia - it's absent in the majority of cases 2, 3
Clinical Application
- ARR is the recommended screening test for primary aldosteronism in patients with resistant hypertension, hypokalemia, incidentally discovered adrenal mass, family history of early-onset hypertension, or stroke at a young age 1
- If primary aldosteronism is confirmed, further evaluation with adrenal venous sampling may be needed to determine if the source is unilateral or bilateral 1, 2
- Treatment options depend on whether the condition is unilateral (typically surgical) or bilateral (typically medical with mineralocorticoid receptor antagonists) 2, 3