Given a plasma renin activity of 0.12 ng/mL/h, an aldosterone‑to‑renin ratio of 66.7, and an aldosterone level of 8 ng/dL, what is the most likely diagnosis and what are the appropriate next diagnostic and treatment steps?

Primary Aldosteronism is the Most Likely Diagnosis

Based on your laboratory values (PRA 0.12 ng/mL/h, aldosterone 8 ng/dL, ARR 66.7), you have a positive screening test for primary aldosteronism that requires confirmatory testing before proceeding to subtype differentiation and treatment.

Interpretation of Your Laboratory Results

Your aldosterone-to-renin ratio (ARR) of 66.7 exceeds the diagnostic threshold, indicating possible primary aldosteronism:

• Converting to standard units: Your aldosterone of 8 ng/dL = 224 pmol/L (multiply by 28) 1
• Your ARR in pmol/L per ng/mL/h: 224 ÷ 0.12 = 1,867 pmol/L/ng/mL/h
• Diagnostic threshold: ARR >550 pmol/L/ng/mL/h is considered positive 1, 2
• Your result: 1,867 is well above the 550 threshold, making primary aldosteronism highly likely

Key Diagnostic Features Present:

• Suppressed renin: PRA of 0.12 ng/mL/h is markedly suppressed (normal renin typically >1.0 ng/mL/h) 3
• Inappropriately normal aldosterone: While your aldosterone of 8 ng/dL may seem "normal," it is inappropriately elevated given your suppressed renin 4. Recent evidence shows that 67% of primary aldosteronism patients have aldosterone <30 ng/dL, and 45% have levels <20 ng/dL 4
• Elevated ARR: Your ratio far exceeds screening thresholds

Next Diagnostic Steps

1. Confirmatory Testing is Mandatory

You must undergo one confirmatory test to definitively establish the diagnosis 5, 6, 7. The guidelines provide four options:

Saline Infusion Test (Most commonly used):

• Infuse 2 liters normal saline over 4 hours
• Primary aldosteronism confirmed if aldosterone fails to suppress to <280 pmol/L (10 ng/dL by immunoassay or 7.5 ng/dL by LC-MS/MS) 1, 6
• Contraindications: Uncontrolled hypertension, heart failure, advanced chronic kidney disease 6

Oral Sodium Loading Test:

• Consume 300 mmol sodium daily for 3 days with 24-hour urine collection on day 3
• Primary aldosteronism confirmed if urinary aldosterone >12 mcg/24h with urinary sodium >200 mEq/24h 1, 6
• Advantage: Can be done outpatient

Captopril Challenge Test:

• Give 50 mg captopril after 1 hour seated rest
• Measure aldosterone and renin at baseline and 2 hours post-captopril
• Primary aldosteronism confirmed if aldosterone fails to suppress to <240 pmol/L (8.6 ng/dL) with suppressed renin 1, 6

Direct Confirmation (May skip confirmatory testing):

• If your ARR >1,400 pmol/L/ng/mL/h AND aldosterone >440 pmol/L (15.7 ng/dL), primary aldosteronism can be diagnosed without additional testing 1
• Your values: ARR 1,867 exceeds 1,400, but aldosterone 224 pmol/L is below 440 pmol/L threshold
• Therefore, you still need confirmatory testing

Important Testing Conditions:

Before confirmatory testing, ensure 1, 3, 6:

• Normalize serum potassium (hypokalemia causes false-negatives)
• Unrestricted salt intake
• Withdraw interfering medications for 4 weeks if possible:
  • Must stop: Spironolactone, eplerenone, amiloride
  • Should stop if feasible: ARBs, ACE inhibitors, beta-blockers, clonidine
  • Can continue: Calcium channel blockers, alpha-blockers

After Confirmatory Testing: Subtype Differentiation

If Primary Aldosteronism is Confirmed:

All patients must undergo adrenal CT scan (3mm contiguous cuts) to 5, 6, 7:

• Exclude adrenocortical carcinoma
• Identify unilateral adenomas
• Guide further management

Adrenal Venous Sampling (AVS):

AVS is mandatory for all surgical candidates over age 35 to differentiate unilateral from bilateral disease 5, 6, 7:

• Unilateral disease (aldosterone-producing adenoma or unilateral hyperplasia): Treat with laparoscopic adrenalectomy
• Bilateral disease (bilateral adrenal hyperplasia): Treat medically with mineralocorticoid receptor antagonists

Why AVS is critical: CT/MRI alone has high false-positive rates (non-functioning incidentalomas) and false-negative rates (unilateral hyperplasia without visible adenoma) in patients >35 years 8, 5, 7

Treatment Pathways

For Unilateral Disease (Post-AVS Confirmation):

Laparoscopic adrenalectomy is the treatment of choice 9, 5, 7:

• Improves blood pressure in virtually 100% of patients
• Cures hypertension in approximately 50%
• Reverses cardiovascular and kidney damage from aldosterone excess
• Eliminates need for lifelong medication

For Bilateral Disease or Non-Surgical Candidates:

Mineralocorticoid receptor antagonists are first-line 9, 5, 7:

• Spironolactone: Start 12.5-25 mg daily, titrate to 50-100 mg daily
• Eplerenone: More selective, fewer side effects; start 25 mg daily, titrate to 50-100 mg daily
• Both effectively lower blood pressure and reverse left ventricular hypertrophy

Why This Diagnosis Matters for Your Outcomes

Primary aldosteronism carries significantly worse cardiovascular outcomes than essential hypertension, even when blood pressure is matched 9, 3:

• 2.8-fold increased risk of stroke
• 2.0-fold increased risk of heart failure
• 4.0-fold increased risk of atrial fibrillation
• 1.7-fold increased risk of coronary artery disease
• Greater kidney damage

These risks are reversible with appropriate treatment (either surgery or mineralocorticoid receptor antagonists), making accurate diagnosis and targeted therapy essential 9, 3.

Common Pitfalls to Avoid

1. Don't assume normal aldosterone excludes primary aldosteronism: Most patients have "inappropriately normal" aldosterone levels in the context of suppressed renin 4

2. Don't skip confirmatory testing: Your ARR is elevated but aldosterone doesn't meet the threshold for direct diagnosis without confirmation 1

3. Don't rely on CT/MRI alone for subtype diagnosis: Imaging without AVS leads to incorrect surgical decisions in patients >35 years 8, 5, 7

4. Don't forget to correct hypokalemia before testing: This causes false-negative results 1, 6

5. Don't use the older ARR cutoff of 20-30 ng/dL per ng/mL/h: When properly converted to pmol/L units, the threshold is 550 pmol/L/ng/mL/h 1, 2