Plasma and Urinary Metanephrines Determined by an Enzyme Immunoassay, but not Serum Chromogranin A for the Diagnosis of Pheochromocytoma in Patients with Adrenal Mass

Adrenal pheochromocytomas are neoplasms characterized by catecholamine excess. Determination of metanephrines by high-pressure liquid chromatography has been well established for the diagnosis of pheochromocytomas, demonstrating high sensitivity and specificity. This study evaluates the diagnostic value of newly available enzyme immunoassays for metanephrines in plasma and urine. Chromogranin A was studied as a potential additional diagnostic tool. Spontaneous blood samples and 24-h urine samples were collected in 149 subjects, including 24 histologically proven pheochromocytomas, 17 aldosterone-secreting and 21 cortisol-secreting adrenal adenomas, 30 nonfunctioning adrenal masses, 15 patients with essential hypertension and 42 healthy normotensive volunteers. Plasma and urinary metanephrine and normetanephrine as well as chromogranin A were determined and putative thresholds were calculated by ROC analysis. Plasma free normetanephrine was found to be the best single parameter with the highest sensitivity (89.5%) and specificity (98.3%) using a threshold of 167 pg/ml. Analysis of the combination of plasma free metanephrines revealed a similar sensitivity with lower specificity of 90.0%. Considering both urinary parameters demonstrated a slightly higher sensitivity (92.9%) with lower specificity (77.6%). ROC analysis revealed a threshold of 215 mu g/l for chromogranin A with rather low sensitivity (73.9%) and specificity (74.2%). A weak positive correlation was found between the tumor size of pheochromocytomas and plasma metanephrine (r = 0.53, p = 0.05) as well as chromogranin A (r = 0.60, p = 0.01). In conclusion, plasma free and urinary metanephrines measured by enzyme immunoassays are convenient and reliable parameters for the diagnosis of pheochromocytoma. In contrast, CgA demonstrated poor sensitivity and specificity.