The value of immunoassays for metanephrines in the biochemical diagnosis of pheochromocytomas.

An undiagnosed pheochromocytoma may result in life-threatening consequences. The diagnosis of pheochromocytoma is based on the overproduction of catecholamines. Highly sensitive biochemical assays are essential to avoid false-negative results. Determinations of 24-h urinary epinephrine and norepinephrine levels are established diagnostic tools. However, they may be falsely negative in patients with a biochemically-silent or periodically-secreting pheochromocytoma. Metanephrines, which are metabolites of catecholamines, have been suggested as an alternative diagnostic tool. Urinary metanephrines are determined by high-pressure liquid chromatography (HPLC) in an increasing number of laboratories, whereas plasma metanephrines measured by HPLC are available in specialised centres only. The different HPLC methods may be cost- and time-intensive. Immunoassays such as radio- or enzyme-immunoassays may be alternative procedures. Measurement of metanephrines instead of catecholamines by either technique improved the diagnostic accuracy for the diagnosis of pheochromocytomas. Determination of plasma free metanephrines demonstrated a higher accuracy than their urinary counterparts. The use of immunoassays may be an alternative to the laborious HPLC, although the method needs to be evaluated in more detail.