Lenders JWM, Keiser HR, Goldstein DS, Willemsen JJ, Friberg P, et al.
Plasma metanephrines in the diagnosis of pheochromocytoma

Ann Int Med (Jul) 123:101-109 1995

The purpose of the study was to determine whether plasma metanephrine measurement offered any advantages over plasma catecholamine or urinary metanephrine measurements. 52 pts with pheo, 51 pts with essential HTN, and 67 normotensives were studied; compairsons were made to pts with secondary hypertension or heart disease. All pts with pheo had elevated plasma metanephrines (100% sensitivity vs. 85% sensitivity for plasma catecholamines). If used to screen a hypertensive population with a much lower prevalence of pheo (much less than 1% in most series), more false positive but few false negative results would be expected.

Plasma free and total metanephrines were measured by HPLC/ED whereas urinary metanephrines were assayed using a colorimetric assay. Sensititivity was 100% for the plasma assay but only 89% for urine; however, this may be explained by different techniques employed. False positive plasma tests occurred in 15% (64% predictive value); The predictive value of the plasma metanephrine test, i.e., percentage of patients with a positive test that truly have the disease, will be even lower, however, if screening hypertensive populations with low prevalence of pheo. (Leehey)

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H: Special problems : Endocrine hypertension