## Diagnosis of Pheochromocytoma **Key Point:** The clinical triad of episodic headaches, sweating, and palpitations in a hypertensive patient is highly suggestive of pheochromocytoma, a catecholamine-secreting tumour causing secondary hypertension. **High-Yield:** 24-hour urinary metanephrines (or plasma free metanephrines) is the **gold standard screening test** for pheochromocytoma due to superior sensitivity (96–99%) and specificity compared to plasma catecholamines, which are unstable and subject to stress-induced elevation. ### Why 24-Hour Urinary Metanephrines? 1. Metanephrines are stable metabolites of epinephrine and norepinephrine 2. Urinary excretion integrates catecholamine secretion over 24 hours, avoiding false negatives from episodic release 3. Less affected by stress, medications, and posture than plasma catecholamines 4. Sensitivity ≥96% when properly collected (patient supine for 30 min before plasma sampling if used) **Clinical Pearl:** A normal 24-hour urinary metanephrine result essentially excludes pheochromocytoma; if suspicion remains high, repeat testing or plasma free metanephrines should be done. ### Investigation Algorithm for Secondary Hypertension ```mermaid flowchart TD A[Hypertension + Episodic symptoms]:::outcome --> B{Clinical clues?}:::decision B -->|Headache, sweating, palpitations| C[Suspect pheochromocytoma]:::outcome B -->|Renal artery bruit, young age| D[Suspect renal artery stenosis]:::outcome B -->|Hypokalaemia, metabolic alkalosis| E[Suspect hyperaldosteronism]:::outcome C --> F[24-hr urine metanephrines]:::action D --> G[Renal artery duplex or CTA]:::action E --> H[Plasma renin & aldosterone ratio]:::action F -->|Elevated| I[Imaging: CT/MRI abdomen]:::action G -->|Stenosis found| J[Angiography ± intervention]:::action ``` [cite:Harrison 21e Ch 297]
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