Initial Testing for Suspected Hyperaldosteronism
The initial test for suspected hyperaldosteronism is a morning plasma aldosterone-to-renin ratio (ARR). 1
Rationale for ARR Testing
The ARR is the preferred initial screening test for hyperaldosteronism due to:
- High negative predictive value for screening primary aldosteronism 1
- Excellent sensitivity and specificity (>90%) when properly performed 1
- Ability to detect cases even without classic presentation of hypokalemia 1
Optimal Testing Conditions
For most accurate results, the ARR should be collected:
- In the morning (ideally after patient has been out of bed for 2 hours)
- After patient has been seated for 5-15 minutes 1
- With the patient in a potassium-replete state 1
Medication Considerations
Certain medications can affect ARR interpretation:
Medications that may interfere with results:
- Mineralocorticoid receptor antagonists (raise aldosterone levels)
- Direct renin inhibitors and β-blockers (lower renin levels) 1
- Diuretics (affect both aldosterone and renin)
Medications with minimal interference:
While traditionally medications were discontinued before testing, evidence suggests ARR can be performed without stopping antihypertensive medications in many cases 3. This approach is particularly valuable for patients with poorly controlled hypertension where medication discontinuation may be risky.
Interpretation of Results
- Positive screening: ARR > 20 with serum aldosterone >16 ng/dL and plasma renin activity (PRA) <0.6 ng/mL per hour 1
- A high ratio (>20) is suggestive of primary aldosteronism, especially in patients taking ACE inhibitors or ARBs 1
- False positives can occur due to low-renin states (volume expansion, dietary salt excess) 1
Follow-up Testing
If ARR is positive, confirmatory testing is required:
Additional Initial Workup
Along with ARR, initial evaluation should include:
- Basic metabolic profile (sodium, potassium, chloride, bicarbonate)
- Assessment of renal function (creatinine)
- Urinalysis 1
Clinical Pearls and Pitfalls
- Primary aldosteronism is more common than previously thought (10-35% of all hypertensive patients) 1
- Despite high prevalence, screening rates remain low (only ~2-4% of eligible patients) 1
- Hypokalemia is a classic but not universal finding; many patients with primary aldosteronism have normal potassium levels 1
- Beta-blockers may cause false-positive results by suppressing renin 2
- ARBs like irbesartan may cause false-negative results (up to 23.5% in some studies) 2
Early detection and treatment of hyperaldosteronism are critical as it is associated with increased cardiovascular morbidity beyond what would be expected from hypertension alone 1, 5.