## Diagnostic Approach to Primary Hyperaldosteronism **Key Point:** The PAC/PRA ratio is the gold-standard screening test for primary hyperaldosteronism. A ratio >20–30 (with absolute PAC >15 ng/dL) has high sensitivity and specificity for the diagnosis. ### Why the PAC/PRA Ratio Works In primary hyperaldosteronism: - Aldosterone is **inappropriately elevated** despite suppressed renin (autonomous production) - The PAC/PRA ratio becomes markedly elevated (typically >20–30) - This distinguishes primary from secondary hyperaldosteronism (where both are elevated proportionally) ### Confirmatory Algorithm ```mermaid flowchart TD A[Resistant HTN + Hypokalemia]:::outcome --> B[Measure PAC and PRA]:::action B --> C{PAC/PRA ratio >20-30?}:::decision C -->|Yes + PAC >15 ng/dL| D[Primary hyperaldosteronism likely]:::outcome C -->|No| E[Secondary HTN / other cause]:::outcome D --> F[Confirmatory test: Saline suppression or captopril challenge]:::action F --> G[CT/MRI abdomen for subtype]:::action ``` **High-Yield:** The PAC/PRA ratio is **screening**; confirmatory tests (saline suppression, captopril challenge) are needed before imaging for subtype (aldosterone-producing adenoma vs. bilateral hyperplasia). **Clinical Pearl:** Hypokalemia in this context is a red flag — it indicates significant aldosterone excess causing renal potassium wasting, making the PAC/PRA ratio even more diagnostic. [cite:Harrison 21e Ch 297]
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