What does a normal aldosterone level with normal plasma renin activity but an elevated aldosterone-to-renin ratio suggest, and how should it be evaluated and managed?

An Elevated Aldosterone-to-Renin Ratio with Normal Individual Values Suggests Possible Primary Aldosteronism and Requires Confirmatory Testing

When both aldosterone and renin levels are within normal ranges but the aldosterone-to-renin ratio (ARR) is elevated, this represents a positive screening test for primary aldosteronism (PA) that warrants further evaluation with confirmatory testing. This scenario occurs because the ARR is fundamentally a screening tool designed to detect inappropriate aldosterone secretion relative to renin suppression, and the ratio can be elevated even when absolute values appear normal 1, 2.

Understanding the Screening Result

The 2020 Hypertension Canada guidelines and the 2025 Endocrine Society guidelines clarify that a positive PA screen requires both conditions to be met 1, 2:

1. Suppressed renin: PRA ≤1 ng/mL/h or DRC ≤8.2 mU/L
2. Elevated ARR:
   • ARR >555 pmol/L per ng/mL/h (or >750 for higher specificity) when using PRA 1
   • ARR >60-70 pmol/L per mU/L when using direct renin concentration 1, 2

The critical insight is that "normal" aldosterone in the presence of suppressed renin is actually inappropriate—in a properly functioning system, low renin should trigger low aldosterone. The elevated ratio captures this dysregulation even when aldosterone hasn't reached overtly elevated levels 2.

Why This Occurs: The Limitations of ARR

Several factors explain this phenomenon:

• ARR is highly dependent on renin levels: The ratio becomes mathematically elevated when renin is low, even with normal aldosterone 3, 4. Research demonstrates that ARR variation is strongly and inversely dependent on PRA (R²=0.71) 3.

• Substantial intra-individual variability: Studies show coefficient of variation of 22-25% for aldosterone and 41-42% for renin and ARR, meaning single measurements may not reflect true status 5. In one study, 38% of confirmed PA patients had at least one ARR below the screening threshold 5.

• Medication effects: ACE inhibitors and ARBs significantly lower ARR, while beta-blockers can falsely elevate it 6. The 2020 guidelines recommend withdrawing interfering medications 4-6 weeks before testing when feasible 1.

Evaluation Algorithm

Step 1: Verify Proper Testing Conditions

Before proceeding, confirm the sample was collected appropriately 1, 2:

• Morning collection after ≥2 hours of ambulation
• Patient seated 5-15 minutes before blood draw
• Hypokalemia corrected (low potassium suppresses aldosterone secretion)
• Sodium intake liberalized
• Interfering medications withdrawn if possible (aldosterone antagonists, potassium-sparing/wasting diuretics for 4-6 weeks; beta-blockers, ACE inhibitors, ARBs for 2 weeks if blood pressure permits)

If conditions were suboptimal, repeat the ARR under standardized conditions before proceeding 1.

Step 2: Assess Clinical Context

Determine if confirmatory testing is indicated based on:

• Hypertension severity and resistance: Patients on ≥3 antihypertensives with uncontrolled blood pressure
• Hypokalemia: Spontaneous or diuretic-induced (though 62% of PA patients are normokalemic)
• Cardiovascular risk: Research suggests ARR ≥1.0 ng/dL per mU/L carries increased CVD risk regardless of absolute aldosterone levels 7

Step 3: Proceed to Confirmatory Testing

The 2025 Endocrine Society guidelines and 2020 Hypertension Canada guidelines both recommend confirmatory testing for positive ARR screens 1, 2. The exception is when spontaneous hypokalemia, undetectable renin, AND aldosterone >440 pmol/L (>16 ng/dL) are all present—then PA is confirmed without additional testing 1, 2.

Choose one confirmatory test 1, 2:

1. Saline loading test (most commonly used):

   • IV: 2L normal saline over 4 hours (recumbent position)
   • PA confirmed if post-infusion aldosterone >280 pmol/L
   • PA excluded if <140 pmol/L
   • Contraindicated in severe uncontrolled hypertension or heart failure

2. Oral sodium loading test:

   • 200 mmol/day sodium for 3 days

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

3. Captopril suppression test:

   • 25-50 mg captopril after 1 hour upright
   • Measure aldosterone at 0 and 1-2 hours
   • PA unlikely if aldosterone suppresses >30%

4. Very high ARR with elevated aldosterone:

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

Management Based on Confirmatory Test Results

If PA is Confirmed:

Proceed to subtype classification to differentiate unilateral from bilateral disease 1:

• Adrenal CT scan (3mm cuts) or MRI for anatomical localization
• Adrenal venous sampling (AVS) if surgery is considered—this is essential because imaging alone cannot reliably distinguish functional from non-functional adenomas 1
• AVS should be performed at experienced centers

Treatment depends on lateralization 1:

• Unilateral disease: Laparoscopic adrenalectomy (curative in many cases)
• Bilateral disease: Mineralocorticoid receptor antagonists (spironolactone 12.5-50 mg daily, titrated to effect; monitor potassium and creatinine)

If PA is Excluded:

Consider alternative explanations for the elevated ARR:

• Low-renin essential hypertension: Common in older patients and certain ethnic groups; may respond well to mineralocorticoid receptor antagonists despite not having PA 8
• Medication effects: Recheck after appropriate medication withdrawal
• Laboratory variability: Consider repeating if clinical suspicion remains high 5

Critical Pitfalls to Avoid

1. Don't dismiss an elevated ARR simply because absolute values are "normal"—the ratio exists precisely to detect inappropriate aldosterone-renin relationships 2, 4

2. Don't rely on a single ARR measurement—variability is substantial, and at least 2 measurements are recommended before excluding PA 5

3. Don't skip confirmatory testing (except in the specific scenario of spontaneous hypokalemia + undetectable renin + aldosterone >440 pmol/L) 1, 2

4. Don't proceed to surgery based on imaging alone—adrenal venous sampling is essential to confirm lateralization in surgical candidates 1

5. Don't forget to correct hypokalemia before testing—low potassium suppresses aldosterone secretion and can cause false-negative results 1, 2

The evidence demonstrates that ARR has limited sensitivity (22-89%) and specificity (67-98%) depending on the cutoff used and testing conditions 4, 6, 9. This underscores why confirmatory testing is mandatory rather than optional when the screening test is positive.