How should low-renin hypertension be evaluated and managed?

Low-Renin Hypertension: Evaluation and Management

Screen for primary aldosteronism (PA) using the aldosterone-to-renin ratio (ARR) as the first-line diagnostic test, followed by confirmatory testing if positive, and treat with mineralocorticoid receptor antagonists (MRAs) regardless of whether formal PA criteria are met, as all patients with low-renin hypertension benefit from aldosterone-targeted therapy. 1, 2

Initial Screening Approach

Who to Screen

Screen patients with low-renin hypertension when they present with:

• Resistant hypertension (uncontrolled on ≥3 drugs)
• Hypertension with hypokalemia (spontaneous or diuretic-induced)
• Adrenal incidentaloma
• Early-onset hypertension (<30 years) or severe hypertension (>180/110 mmHg)
• Family history of early stroke or hypertension 1, 3

Screening Test: Aldosterone-to-Renin Ratio (ARR)

Collection conditions are critical 1:

• Morning sample after patient ambulatory (sitting, standing, walking) for ≥2 hours
• Patient seated 5-15 minutes before blood draw
• Correct hypokalemia and liberalize sodium intake first
• Withdraw interfering medications 4-6 weeks before testing:
  • Must stop: Aldosterone antagonists, potassium-sparing/wasting diuretics
  • Ideally stop (if BP controllable): Beta-blockers, ACE inhibitors, ARBs, renin inhibitors, dihydropyridine calcium channel blockers, centrally-acting alpha-2 agonists
• Can continue: Slow-release verapamil, diltiazem, hydralazine, prazosin, doxazosin, terazosin
• Discontinue oral contraceptives 1 month before testing (causes false positives with direct renin concentration) 1

Interpretation cutoffs 1:

• Plasma renin activity method: ARR >555 pmol/L per ng/mL/h (higher sensitivity) or >750 (higher specificity)
• Direct renin concentration (mIU/L): ARR >60 (higher sensitivity) or >91 (higher specificity)
• Direct renin concentration (ng/L): ARR >100 (higher sensitivity) or >144 (higher specificity)

Confirmatory Testing

A positive screening ARR requires confirmatory testing unless the patient has spontaneous hypokalemia with plasma aldosterone >440 pmol/L (>16 ng/dL) and suppressed renin—this combination confirms PA without additional testing 4.

Confirmatory Test Options (Choose One) 1

1. Intravenous saline suppression test (most commonly used):

   • Administer 2L normal saline IV over 4 hours, patient recumbent
   • Contraindicated: Severe uncontrolled hypertension or heart failure
   • PA confirmed: Post-infusion aldosterone >280 pmol/L (>10 ng/dL)
   • PA excluded: <140 pmol/L (<5 ng/dL)

2. Oral salt loading test:

   • 200 mmol/day sodium (>5g/day sodium, >12g/day salt, >2 tsp/day) for 3 days

   • PA confirmed: 24-hour urinary aldosterone >33 nmol/day (measured day 3-4)
   • PA excluded: <28 nmol/day

3. Captopril suppression test:

   • 25-50 mg captopril orally after 1 hour sitting/standing
   • Measure renin and aldosterone at baseline and 1-2 hours post-dose
   • PA unlikely: Aldosterone suppressed >30%
   • PA likely: Aldosterone remains elevated, renin remains suppressed

4. Highly elevated ARR with high aldosterone:

   • ARR >1400 pmol/L per ng/mL/h (or >270 pmol/L per ng/L) AND aldosterone >440 pmol/L (>16 ng/dL) confirms PA without additional testing 1

The Spectrum Reality: PA vs. Low-Renin Essential Hypertension

Here's the critical clinical insight: Recent evidence demonstrates a continuous spectrum between low-renin essential hypertension and PA, rather than distinct categories 4, 5, 6. The 2025 study showed that 57-95% of patients with low-renin hypertension meet PA criteria depending on which confirmatory test interpretation is used, yet 86.5-91.7% respond to aldosterone-targeted therapy regardless of formal PA diagnosis 6.

This means the traditional diagnostic algorithm may be unnecessarily laborious for clinical practice. The key therapeutic principle: All patients with suppressed renin benefit from MRA therapy, whether they meet strict PA criteria or not 7, 2, 5.

Subtype Classification (If Surgery Considered)

Only pursue if patient is surgical candidate and desires surgery 1, 2:

1. Adrenal CT scan (3mm contiguous cuts) or MRI to identify adenomas
2. Adrenal venous sampling (AVS) is mandatory before surgery if imaging shows:
   • Bilateral lesions
   • Normal-appearing adrenals
   • Any uncertainty about lateralization
   • AVS should only be performed at experienced centers 1

Unilateral disease → Laparoscopic adrenalectomy (cures hypertension in ~50%, improves in virtually 100%) 3

Bilateral disease or non-surgical candidate → Medical therapy with MRAs 3, 2

Treatment: Aldosterone-Targeted Therapy

First-Line: Mineralocorticoid Receptor Antagonists 7, 2

Spironolactone (preferred, more potent):

• Starting dose: 12.5-25 mg daily (higher if severe hypokalemia: 50 mg daily)
• Titration: Increase by 25-50 mg every 8-12 weeks
• Target dose: 50-100 mg daily (most patients achieve renin de-suppression at this range)
• Maximum effect: Takes up to 3 months
• Side effect: Dose-related gynecomastia (especially >50 mg/day in men)

Eplerenone (alternative, better tolerated in men):

• Starting dose: 25 mg once or twice daily
• Titration: Increase by 25-100 mg increments
• Less potent than spironolactone, requires higher doses

Monitoring Protocol 2

Initial phase (first 2-3 months):

• Check electrolytes, creatinine, renin at 2-3 months after starting
• Discontinue potassium supplements at days 2-4 (hypokalemia usually resolves rapidly)
• More frequent monitoring if severe baseline hypokalemia or renal impairment

Titration phase:

• Adjust MRA dose every 8-12 weeks based on BP response
• Recheck electrolytes, creatinine, renin 2-3 months after each dose change
• Goal: De-suppress renin (normalize renin levels) AND control BP
• Once renin normalized, if BP still elevated, add non-MRA antihypertensives rather than further increasing MRA

Long-term maintenance:

• Annual potassium and creatinine
• Regular BP monitoring

Alternative: Amiloride (Epithelial Sodium Channel Blocker) 7

Amiloride 10 mg daily (or amiloride 2.5-5 mg/hydrochlorothiazide 25 mg combination):

• Particularly effective in low-renin hypertension
• Reduced systolic BP by 31 mmHg and diastolic by 15 mmHg in one study
• Advantage: No gynecomastia
• Disadvantage: Less widely available, less studied than spironolactone

Critical Pitfalls to Avoid

1. High dietary sodium intake is the most common reason for apparent MRA non-response—explicitly counsel patients on salt restriction (<5g/day sodium) 2

2. GFR may decrease initially with MRA therapy—this is usually a marker of treatment efficacy (reduced hyperfiltration), not harm. Monitor but don't panic unless progressive decline 2

3. Don't over-diagnose hyperkalemia risk—it's uncommon with MRAs alone, but increases with concurrent ACE inhibitors/ARBs, NSAIDs, diabetes, or CKD. Consider discontinuing ACE inhibitors/ARBs when starting MRAs 2

4. Don't pursue exhaustive PA diagnostics in all patients with low-renin hypertension—empirical MRA therapy is appropriate and effective even without confirmed PA 6

5. Medication interference with screening is real—don't screen patients on aldosterone antagonists, and ideally withdraw other interfering drugs if safely possible 1

Practical Algorithm Summary

Step 1: Measure ARR under proper conditions

• If ARR elevated → Proceed to Step 2
• If ARR normal but renin suppressed → Consider empirical MRA trial

Step 2: Confirmatory testing (saline suppression most practical)

• If confirmed PA → Proceed to Step 3
• If not confirmed but renin suppressed → Consider empirical MRA trial anyway 6

Step 3: Subtype classification (only if surgery desired)

• CT/MRI → AVS if considering surgery
• Unilateral → Surgery
• Bilateral or non-surgical → Medical therapy

Step 4: Medical therapy with spironolactone 12.5-25 mg daily

• Titrate every 8-12 weeks to normalize renin and control BP
• Monitor electrolytes and creatinine
• Emphasize dietary salt restriction

The evidence strongly supports that all patients with low-renin hypertension benefit from aldosterone-targeted therapy, making the distinction between "true PA" and "low-renin essential hypertension" less clinically relevant than previously thought 5, 8, 6.