THE URINARY METANEPHRINE-TO-CREATININE RATIO FOR THE DIAGNOSIS OF PHEOCHROMOCYTOMA

Objective: To compare the operating characteristics of two tests for d iagnosing pheochromocytoma: 1) measurement of the ratio between urinar y metanephrine and creatinine levels and 2) measurement of urinary met anephrine levels alone. A second objective was to ascertain the reason s for false-positive test results. Design: Cross-sectional study. Sett ing: Hypertension referral center. Patients: 1013 patients referred fo r hypertension and tested for pheochromocytoma. Measurements: 24-hour urinary levels of metanephrine (measured using liquid chromatography) and creatinine. The presence of pheochromocytoma was confirmed at surg ery. In patients with positive test results, the absence of pheochromo cytoma was documented by negative results of retests and imaging proce dures. Results: Of 58 patients with increased metanephrine levels or i ncreased metanephrine-to-creatinine ratios, 20 had pheochromocytoma an d 38 did not. Of the 38 patients without pheochromocytoma, 15 had high metanephrine levels but normal metanephrine-to-creatinine ratios. The respective operating characteristics of measurement of urinary metane phrine levels and measurement of the metanephrine-to-creatinine ratio were as follows: sensitivity, 95% and 100%; specificity, 98% and 98%; positive predictive value, 46% and 47%; and negative predictive value, 100% and 100%. In 13 of the 23 patients who had a high metanephrine-t o-creatinine ratio, various acute events may have caused hypersecretio n of catecholamines. Conclusions: Measurement of the metanephrine-to-c reatinine ratio is a sensitive and specific test for pheochromocytoma, However, acute events may increase urinary metanephrine excretion to the level that occurs with tumors.