- Plasma Metanephrines
- Quantitative Metanephrines
Diagnose pheochromocytoma, a catecholamine-secreting tumor of the adrenal medulla.
Measurement of plasma-free metanephrines has been recognized as a superior assay over traditional methods for detection of pheochromocytoma. The advantage stems from the more direct correlation of plasma-free metanephrine concentration to the catecholamine and metanephrine production of adrenomedullary and pheochromocytoma cells than from other sources. Plasma-free metanephrines yield fewer false-positive results than other assays and can be used as an indicator of a pheochromocytoma’s progression. It has been shown that the underlying cause of hypertension in 0.1% to 0.5% of the hypertensive population may be due to pheochromocytoma. Historically, assays such as urinary metanephrines, urinary vanillylmandelic acid (VMA), and urinary or plasma catecholamines have been used for this diagnosis. Individually, none of these assays provides sufficient specificity and multiple assays are often required. False-negative and false-positive results occur with higher instance than with plasma metanephrines.
Lavender-top (EDTA) tube
Patient should be fasting overnight (water and noncaffeinated soft drinks are permissible). The patient should be in a supine position for at least 15 minutes before and during sample collection. An indwelling venous catheter (normal saline to keep the line patent) is recommended, since the acute effects of the stress of venipuncture may increase metanephrine. It is preferable, but not essential, to draw the sample without a tourniquet.
Draw blood in chilled lavender-top (EDTA) tube. Invert to mix with preservatives. Centrifuge and transfer the plasma to a labeled plastic transport tube (Note: The whole blood sample may be kept refrigerated at 4°C for as long as two hours before centrifugation, if necessary).