The Value of Immunoassays for Metanephrines in the Biochemical Diagnosis of Pheochromocytomas

Abstract

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.

Key words

plasma metanephrines - urinary metanephrines - pheochromocytoma - HPLC - immunoassays

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