Evaluation and Management of Low Plasma Renin Activity

Clinical Significance

• Low plasma renin activity indicates volume‑mediated (“V‑type”) hypertension or autonomous aldosterone production, highlighting the need to assess for primary aldosteronism. 1, 2
• When aldosterone excess co‑exists, suppressed renin is linked to higher cardiovascular morbidity. 1

When to Screen for Primary Aldosteronism

• Hypertension with spontaneous or diuretic‑induced hypokalemia – screen by measuring aldosterone and calculating the aldosterone‑to‑renin ratio (ARR). 3
• Resistant hypertension (BP ≥ 140/90 mmHg on ≥ 3 antihypertensive agents, including a diuretic) – screen with ARR. 4
• Hypertension with an adrenal incidentaloma – screen with ARR. 1
• Hypertension accompanied by atrial fibrillation without structural heart disease – screen with ARR. 2, 5

Standardized Testing Conditions

• Collect blood samples in the morning after the patient has been seated for ≥ 15 minutes. 6
• Ensure unrestricted dietary salt intake before sampling. 2
• Correct hypokalemia prior to testing to avoid false‑negative results. 3
• Withdraw interfering medications (aldosterone antagonists, ARBs, beta‑blockers, clonidine) for 2–4 weeks when safe. 1, 2
  
  • Medications that must be stopped: aldosterone antagonists (spironolactone, eplerenone), ARBs, beta‑blockers, clonidine. 4
  • Medications that may be continued: alpha‑1 blockers, long‑acting non‑dihydropyridine calcium channel blockers, hydralazine. 3

Interpretation of the Aldosterone‑to‑Renin Ratio (ARR)

• Positive screening is defined by either:
  
  • ARR > 550 pmol/L per ng/mL/h (Canadian guideline) or
  • ARR > 30 when aldosterone is expressed in ng/dL and PRA in ng/mL/h (ACC/AHA guideline). 1
• Plasma aldosterone must be ≥ 10 ng/dL (277 pmol/L) for the ARR to be considered positive, because very low renin alone can inflate the ratio. 1, 4

Criteria for Overt Primary Aldosteronism (No Confirmatory Test Needed)

• Plasma renin activity < 0.2 ng/mL/hand plasma aldosterone > 15 ng/dL (416 pmol/L) by LC‑MS/MS or > 20 ng/dL (554 pmol/L) by immunoassay. 5
• Must be accompanied by resistant hypertension or spontaneous hypokalemia. 3

Confirmatory Testing (When ARR Positive but Not Overt)

Alternative confirmatory criterion (no additional test): ARR > 1400 pmol/L per ng/mL/h with plasma aldosterone > 440 pmol/L. 2

Alternative Diagnoses That Can Mimic Low‑Renin Primary Aldosteronism

• Chronic kidney disease – nephron loss reduces renin, potentially yielding a false‑positive ARR. 5
• Medications such as beta‑blockers and centrally acting α‑2 agonists suppress renin and may cause false‑positive screening. 5

Treatment Strategies

If Primary Aldosteronism Is Confirmed

• Subtype classification with adrenal CT/MRI and adrenal venous sampling to differentiate unilateral from bilateral disease. 1, 2
• Unilateral disease – laparoscopic adrenalectomy improves blood pressure in virtually all patients and cures hypertension in ~50 %. 1, 4
• Bilateral disease or non‑surgical candidates – mineralocorticoid receptor antagonists (spironolactone or eplerenone) are first‑line agents. 1, 2, 4

If Primary Aldosteronism Is Excluded (Low‑Renin Hypertension)

• Use anti‑volume (“anti‑V”) drugs: thiazide‑type diuretics, calcium‑channel blockers, alpha‑1 blockers, or low‑dose spironolactone. 4
• Avoid “anti‑R” drugs that raise renin (ACE inhibitors, ARBs, beta‑blockers). 4

Common Pitfalls and Recommendations

• Correct hypokalemia before screening; otherwise the ARR may be falsely negative. 2, 3
• Do not rely on low renin alone; simultaneous aldosterone measurement is mandatory for interpretation. 1, 5
• Do not accept a positive ARR while patients are on interfering medications; repeat testing after appropriate drug withdrawal. 5
• Do not skip confirmatory testing in borderline cases, as very low renin can generate false‑positive screens. 5, 3

Guidelines for Screening, Confirmation, and Management of Primary Aldosteronism

1. Screening Thresholds and Interpretation of the ARR

• The U.S. Endocrine Society (2025) recommends using an aldosterone‑renin ratio (ARR) > 30 (ng/dL per ng/mL/h) as the primary screening cutoff for primary aldosteronism. 9
• Canadian guidelines (2007 & 2008) define a positive screen as ARR > 550 pmol/L per ng/mL/h (≈ 20 when aldosterone is expressed in ng/dL). 10, 11
• An ARR of 50 exceeds both the U.S. and Canadian thresholds, indicating a high likelihood of primary aldosteronism. 9
• For the ARR to be considered truly positive, the absolute plasma aldosterone concentration must be ≥ 10 ng/dL (≈ 277 pmol/L). 9

2. When No Confirmatory Test Is Required

• If aldosterone is > 20 ng/dL (≈ 554 pmol/L) by immunoassay or > 15 ng/dL (≈ 416 pmol/L) by LC‑MS/MS, the diagnosis of overt primary aldosteronism can be made without additional confirmatory testing; patients should proceed directly to subtype classification with adrenal imaging and adrenal venous sampling. 9
• This “no‑test” pathway also requires a suppressed PRA (< 0.2 ng/mL/h) together with resistant hypertension or spontaneous hypokalemia. 10, 9

3. Confirmatory Testing (Aldosterone 10–20 ng/dL)

• When aldosterone lies between 10 ng/dL and 20 ng/dL (277–554 pmol/L), one confirmatory test should be performed. Acceptable tests and their positive criteria are:

• An alternative “high‑ARR” rule allows diagnosis without a confirmatory test when ARR > 1400 pmol/L per ng/mL/h (≈ 50) and aldosterone > 440 pmol/L (≈ 16 ng/dL). 10, 11

4. Excluding Primary Aldosteronism

• If aldosterone is < 10 ng/dL (≈ 277 pmol/L), primary aldosteronism is excluded; the low renin reflects volume‑mediated (“V‑type”) hypertension, best managed with thiazide diuretics, calcium‑channel blockers, or α‑1 blockers, while avoiding ACE inhibitors, ARBs, and β‑blockers. 9

5. Pre‑Test Standardization Requirements

• Sample timing: Morning blood draw after the patient has been seated for ≥ 15 minutes. 10, 11
• Potassium status: Correct hypokalemia before testing, as low potassium suppresses aldosterone and may cause false‑negative results. 9, 12
• Medication wash‑out (2–4 weeks if safe): Discontinue spironolactone, eplerenone, ARBs, β‑blockers, and clonidine; continuation of α‑1 blockers, long‑acting non‑DHP calcium‑channel blockers, and hydralazine is permissible. 10, 11, 9, 12
• Dietary salt: Ensure unrestricted dietary sodium intake on the testing day. 12
• If any of these conditions are not met, repeat the ARR under standardized conditions; β‑blockers, in particular, can inflate the ARR and cause false‑positive screens in up to 38 % of cases. 10, 11, 9

6. Special Considerations

• Chronic kidney disease: Nephron loss reduces renin proportionally, increasing the risk of false‑positive ARR results; therefore, interpretation should be cautious and confirmatory testing emphasized. 9

7. Subtype Classification After Confirmation

• All patients with confirmed primary aldosteronism should undergo adrenal CT or MRI to exclude adrenocortical carcinoma and to identify unilateral adenomas. 10, 11, 13, 9
• Patients > 35 years old or those with bilateral/normal imaging must proceed to adrenal venous sampling (AVS) to differentiate unilateral from bilateral disease, because imaging alone has high false‑positive and false‑negative rates. 10, 11, 13, 9

7.1 Treatment Based on Subtype

• Unilateral disease: Laparoscopic adrenalectomy cures hypertension in ~ 50 % of patients and improves blood pressure in virtually all treated individuals. 9
• Bilateral disease or non‑surgical candidates: First‑line therapy consists of mineralocorticoid‑receptor antagonists (spironolactone 25–100 mg/day or eplerenone 50–100 mg/day). 9