## Biochemical Diagnosis and Genetics of Pheochromocytoma ### The Correct Answer (Option 4) **Key Point:** Plasma chromogranin A is NOT the primary diagnostic test and has poor specificity. It is elevated in many neuroendocrine tumors, renal failure, proton pump inhibitor use, and other conditions. Plasma free metanephrines are the gold standard for initial screening. **Warning:** Chromogranin A is a useful confirmatory marker but NOT a first-line diagnostic tool. Many students confuse its role as a tumor marker with diagnostic utility. ### Why the Other Options Are Correct | Statement | Evidence | |-----------|----------| | **Plasma free metanephrines** | >95% sensitivity; >89% specificity; unaffected by posture, activity, or medications; first-line test per Endocrine Society guidelines | | **24-hour urine metanephrines** | Sensitivity 89–99% but lower than plasma; acceptable alternative if plasma unavailable; requires proper collection and patient preparation | | **Genetic testing in all patients** | 30–40% of pheochromocytomas are hereditary (SDH, VHL, RET, NF1); recommended in all to identify syndromic disease and guide family screening | **High-Yield:** Plasma free metanephrines > 24-hour urine metanephrines > plasma catecholamines (poor sensitivity) > chromogranin A (poor specificity). **Mnemonic:** **PUMA** — **P**lasma metanephrines first, **U**rine metanephrines second, **M**ass imaging third, **A**ddress genetics always. **Clinical Pearl:** Chromogranin A rises with PPI use (very common in India) — a major source of false positives. Always check medication history before ordering. [cite:Endocrine Society Clinical Practice Guidelines: Pheochromocytoma and Paraganglioma (2014)]
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