The diagnostic utility of different thresholds of elevated urinary fractionated metanephrine (UFM) for pheochromocytoma-paraganglioma (PPGL) was evaluated in 10 164 community-dwelling subjects (2012-2017). Levels were ≥1.5× the upper normal limit (UNL) in 276 subjects (2.7%) and ≥2×UNL in 138 (1.4%). PPGL was subsequently diagnosed in 59 (mean age 51.9 ± 14.3, 64% female); 58 (98.3%) with UFM ≥ 2×UNL. Positive predictive values (PPV) were 42% for UFM ≥ 2×UNL, 55% for UFM ≥ 2.5×UNL, and 69% for UFM ≥ 3×UNL. The main reason for PPGL screening (52.5%) was adrenal incidentaloma. Mean (median) metanephrine/normetanephrine levels were 6.7 ± 9×UNL (3 × UNL) and 6.1 ± 8.9×UNL (2.5 × UNL). Six patients (10.2%) had an extra-adrenal tumor (one malignant paraganglioma); one had bilateral pheochromocytoma. Only one patient presented with the "classic triad" (headache, palpitations, sweating). In conclusion, after excluding obvious reasons for false-positive results, thorough diagnostic assessment for PPGL is justified in all subjects with UFM ≥ ×2UNL. The PPV of milder UFM elevations is very low.
Keywords: adrenal incidentaloma; false positive; pheochromocytoma; positive predictive value.
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