Normal Aldosterone/PRA Ratio Values
A normal aldosterone-to-renin ratio (ARR) is generally considered to be below 550 pmol/L per ng/mL/h when using plasma renin activity (PRA), or below 70 pmol/L per mU/L when using direct renin concentration (DRC). 1, 2, 3, 4, 5
Standardized Measurement Conditions
The ARR must be measured under specific conditions to ensure accuracy:
- Morning collection (more than 2 hours after awakening)
- Seated position after resting 5-15 minutes
- Normal dietary sodium intake (not restricted)
- Normal serum potassium (hypokalemia suppresses aldosterone and causes false negatives)
- Standardized medication management (see below)
Unit-Specific Thresholds
The most recent 2025 Endocrine Society guideline provides clear thresholds based on measurement method 5:
When Aldosterone is Measured by Immunoassay:
- ARR > 20 (when aldosterone in ng/dL and PRA in ng/mL/h)
- ARR > 70 (when aldosterone in pmol/L and DRC in mU/L)
When Aldosterone is Measured by LC-MS/MS:
- ARR thresholds are approximately 25% lower than immunoassay values
Canadian Guidelines Thresholds:
- ARR > 550 pmol/L per ng/mL/h for PRA
- ARR > 140 pmol/L per ng/L for direct renin concentration
Critical Interpretation Points
A positive screen requires BOTH conditions:
- Suppressed renin (the hallmark finding)
- Elevated ARR above the threshold
Additionally, to avoid false positives from very low renin values 7:
- Apply ARR calculation only if aldosterone > 240 pmol/L (9 ng/dL)
- Set minimum renin values: DRC < 5 mU/L should be calculated as 5 mU/L, and PRA < 0.2 ng/mL/h should be calculated as 0.2 ng/mL/h
Important Caveats
Medication Effects:
The 2016 French consensus and 2025 Endocrine Society guidelines emphasize that certain medications significantly interfere with ARR 6, 5:
Must withdraw (if safe):
- Mineralocorticoid receptor antagonists (4 weeks)
- Diuretics including amiloride/triamterene (4 weeks)
- ACE inhibitors and ARBs (2 weeks)
May cause false positives (lower renin):
- Beta-blockers
- Clonidine and central alpha-2 agonists
High Intra-individual Variability:
Recent research demonstrates substantial variability in ARR measurements, with coefficient of variation of 41-42% 8. This supports repeating the test on a different day before excluding primary aldosteronism, especially when:
- Initial screen is negative but pretest probability is moderate-to-high
- Hypokalemia is present
- Interfering medications were not withdrawn
- Renin is suppressed with aldosterone 5-10 ng/dL (138-277 pmol/L)
Age and Sex Considerations:
Research shows that women aged 20-39 years have significantly higher ARR than men (median 20.7 vs 10.3), despite lower blood pressure 9. Population-based studies suggest upper reference limits vary by age and sex, ranging from 14.2 to 25.5 in healthy individuals 10. However, current guidelines do not incorporate age/sex-specific thresholds.
When Confirmatory Testing is NOT Needed
The 2016 French consensus provides specific scenarios where diagnosis can be made or excluded without dynamic testing 6:
PA can be diagnosed without confirmatory testing:
- Elevated ARR on two separate occasions AND
- Plasma aldosterone > 550 pmol/L (20 ng/dL) on both measurements
PA can be excluded without confirmatory testing:
- Normal ARR on two separate occasions AND
- Plasma aldosterone < 240 pmol/L (9 ng/dL) on both measurements
All other patients require dynamic confirmatory testing (saline infusion test preferred).