Interpretation and Management of PRA 0.24 ng/mL/h with ARR 50
Your patient has a positive screen for primary aldosteronism that requires confirmatory testing before proceeding to subtype classification and treatment. 1
Understanding the Results
Your patient's plasma renin activity of 0.24 ng/mL/h is suppressed (normal range typically 0.5–3.3 ng/mL/h), and the aldosterone-to-renin ratio of 50 is elevated above screening thresholds used in most guidelines. 2, 3
ARR Threshold Interpretation
- Canadian guidelines define a positive screen as ARR > 550 pmol/L per ng/mL/h (approximately 20 when aldosterone is in ng/dL and PRA in ng/mL/h). 2, 3
- U.S. Endocrine Society 2025 guidelines use ARR > 30 (ng/dL per ng/mL/h) as the screening threshold. 1
- Your ARR of 50 exceeds both thresholds, making primary aldosteronism likely. 1, 4
Critical Requirement: Aldosterone Level
You must know the absolute plasma aldosterone concentration to interpret this ARR properly. 1, 4 The ARR can be falsely elevated when renin is very low but aldosterone remains normal. Guidelines require:
- Aldosterone ≥ 10 ng/dL (277 pmol/L) for the ARR to be considered truly positive. 1, 4
- If aldosterone is < 10 ng/dL despite the elevated ARR, primary aldosteronism is unlikely and the low renin reflects volume-mediated hypertension. 4
Next Steps Based on Aldosterone Level
If Aldosterone > 20 ng/dL (554 pmol/L) by Immunoassay or > 15 ng/dL (416 pmol/L) by LC-MS/MS
No confirmatory testing is needed. 1, 4 This combination of:
- PRA < 0.2 ng/mL/h (your patient is 0.24, borderline)
- Aldosterone > 15–20 ng/dL
- Plus resistant hypertension or spontaneous hypokalemia
constitutes overt primary aldosteronism and you should proceed directly to subtype classification with adrenal CT and adrenal venous sampling. 1, 4
If Aldosterone 10–20 ng/dL (277–554 pmol/L)
Perform one confirmatory test to document autonomous aldosterone secretion. 2, 3, 1 Choose from:
| Test | Procedure | Positive Result |
|---|---|---|
| Intravenous saline suppression | Infuse 2 L normal saline over 4 hours | Post-infusion aldosterone > 280 pmol/L (10 ng/dL) [2,3] |
| Oral salt loading | 300 mmol sodium/day × 3 days | 24-hour urinary aldosterone > 33 nmol/day (12 µg/day) with urinary sodium > 200 mEq [2,3] |
| Captopril suppression | 25–50 mg captopril orally | Aldosterone fails to suppress > 30% or remains > 240 pmol/L at 2 hours [2,3,1] |
| Fludrocortisone suppression | 0.25 mg/day × 2 days plus oral sodium loading | Aldosterone ≥ 140 pmol/L (5 ng/dL) [2,3] |
Alternative criterion (no additional test needed): ARR > 1400 pmol/L per ng/mL/h (approximately 50 in ng/dL per ng/mL/h units) with aldosterone > 440 pmol/L (16 ng/dL). 2, 3 If your patient's aldosterone exceeds 16 ng/dL, the diagnosis is confirmed without further testing.
If Aldosterone < 10 ng/dL (277 pmol/L)
Primary aldosteronism is excluded. 1, 4 The low renin reflects volume-mediated ("V-type") hypertension. Treat with thiazide diuretics, calcium channel blockers, or alpha-1 blockers; avoid ACE inhibitors, ARBs, and beta-blockers. 4
Pre-Test Requirements (If Not Already Done)
Before accepting these results as valid, confirm the following conditions were met: 2, 3, 1, 5
- Morning sample collected after patient seated ≥ 15 minutes 2, 3
- Hypokalemia corrected (low potassium suppresses aldosterone and causes false-negatives) 1, 5, 4
- Interfering medications withdrawn for 2–4 weeks if safe: 2, 3, 1, 5
- Must stop: spironolactone, eplerenone, ARBs, beta-blockers, clonidine
- May continue: alpha-1 blockers, long-acting non-dihydropyridine calcium channel blockers, hydralazine
- Unrestricted dietary salt intake 5
If these conditions were not met, repeat the ARR under standardized conditions. 2, 3, 1 Beta-blockers in particular suppress renin and inflate the ARR, causing false-positive screens in up to 38% of cases. 6, 7
Important Caveats
ARR Variability
The ARR has substantial intra-individual variability (coefficient of variation 41–42%), and 38% of patients with confirmed primary aldosteronism have at least one ARR below the screening threshold. 8 If clinical suspicion remains high (resistant hypertension, hypokalemia, adrenal incidentaloma), repeat the ARR on a separate day even if the first result is borderline. 8
Chronic Kidney Disease
Nephron loss lowers renin proportionately, leading to false-positive ARR screens in CKD patients. 1, 4 If your patient has CKD, interpret the ARR cautiously and rely more heavily on confirmatory testing.
Race-Specific Performance
The ARR has lower sensitivity in African American patients (75% vs. 80% in whites) but maintains a high negative predictive value (92%). 7 A negative ARR effectively rules out primary aldosteronism regardless of race. 7
After Confirmation: Subtype Classification
Once primary aldosteronism is confirmed, all patients require adrenal CT or MRI to exclude adrenocortical carcinoma and identify unilateral adenomas. 2, 3, 9, 1
Patients over 35 years old or with bilateral/normal imaging must undergo adrenal venous sampling to differentiate unilateral from bilateral disease, because imaging alone has high false-positive and false-negative rates. 2, 3, 9, 1
- Unilateral disease: Laparoscopic adrenalectomy cures hypertension in ~50% and improves blood pressure in virtually all patients. 1, 4
- Bilateral disease or non-surgical candidates: Mineralocorticoid receptor antagonists (spironolactone 25–100 mg/day or eplerenone 50–100 mg/day) are first-line therapy. 1, 4