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.