## Screening for Primary Aldosteronism in Resistant Hypertension ### Clinical Context Primary aldosteronism accounts for 5–10% of hypertension cases and up to 20% of resistant hypertension. Early detection is critical because it is surgically curable in 30–40% of cases (aldosterone-producing adenoma). ### Why Plasma Aldosterone-to-Renin Ratio (ARR)? **Key Point:** The plasma aldosterone concentration (PAC) to plasma renin activity (PRA) ratio is the gold-standard screening test for primary aldosteronism. It is non-invasive, cost-effective, and has excellent sensitivity and specificity. **High-Yield:** - **ARR threshold:** ARR > 20–30 (depending on assay units) suggests primary aldosteronism - **Sensitivity:** ~90% for detecting aldosterone-producing adenoma - **Specificity:** ~80% when combined with elevated PAC (>15 ng/dL) - **Timing:** Perform in morning after 30 minutes of upright posture (sitting or standing) **Clinical Pearl:** ARR is superior to absolute PAC or PRA alone because it corrects for variations in renin-angiotensin system activity and accounts for the physiologic inverse relationship between aldosterone and renin. ### Diagnostic Algorithm for Primary Aldosteronism ```mermaid flowchart TD A[Resistant hypertension or hypokalemia]:::outcome --> B[Calculate ARR]:::action B --> C{ARR > 20-30?}:::decision C -->|No| D[Primary aldosteronism unlikely]:::outcome C -->|Yes| E{PAC > 15 ng/dL?}:::decision E -->|No| F[False positive ARR, repeat testing]:::action E -->|Yes| G[Confirmatory test needed]:::action G --> H{Captopril challenge or saline suppression?}:::decision H -->|Positive| I[Adrenal imaging: CT or MRI]:::action I --> J{Unilateral adenoma?}:::decision J -->|Yes| K[Adrenal vein sampling if surgical candidate]:::action J -->|No| L[Bilateral hyperplasia: medical management]:::action ``` ### Comparison of Screening vs. Confirmatory Tests | Test | Role | Sensitivity | Specificity | Limitations | |---|---|---|---|---| | **ARR (PAC/PRA)** | **Screening** | ~90% | ~80% | Affected by medications, hypokalemia, time of day | | Captopril challenge | Confirmatory | 90% | 85% | Requires ACE inhibitor dose; time-consuming | | Saline suppression | Confirmatory | 95% | 90% | Requires IV access; volume expansion risk | | Adrenal CT | Localization | 80% | 95% | Cannot distinguish adenoma from hyperplasia; radiation | | Adrenal vein sampling | Lateralization | 99% | 99% | Invasive; requires expertise; gold standard for lateralization | ### Pre-Test Considerations **Warning:** Medications and electrolytes affect ARR accuracy: - **Stop/adjust:** ACE inhibitors, ARBs, beta-blockers, thiazide diuretics (if possible) 2–4 weeks before testing - **Correct:** Hypokalemia (K^+^ < 3.5 mEq/L) before testing — low potassium suppresses aldosterone - **Maintain:** Adequate sodium intake (>3 g/day) to avoid suppressing aldosterone **Mnemonic: SAFE Screening** — **S**creening with ARR, **A**djust medications, **F**ix electrolytes, **E**valuate confirmatory test if positive. ### Why Other Options Are Suboptimal **Adrenal CT scan:** Localization tool, not screening. Used AFTER biochemical confirmation. Cannot distinguish adenoma from hyperplasia; 10–15% of normal individuals have incidental adenomas. **Captopril challenge test:** Valid confirmatory test but requires ACE inhibitor dosing and is more cumbersome than ARR for initial screening. Reserved for borderline ARR results. **24-hour urine aldosterone & sodium:** Useful for research and confirmation but less practical for screening. Requires accurate 24-hour collection; affected by sodium intake variability. **Tip:** In resistant hypertension, always screen for primary aldosteronism before pursuing extensive imaging or considering additional antihypertensive agents. Early diagnosis can lead to curative surgery in adenoma cases.
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