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Metanephrines, Fractionated, Plasma Free
- Plasma Metanephrines
- Quantitative Metanephrines
Diagnose pheochromocytoma, a catecholamine-secreting tumor of the adrenal medulla
Liquid chromatography/tandem mass spectrometry (LC/MS-MS)
Normetanephrine: 0−145 pg/mL; metanephrine: 0−62 pg/mL
Concentrations of normetanephrine between 146 and 487 pg/mL and metanephrine between 63 and 255 pg/mL are considered indeterminate. Follow-up biochemical testing is recommended when patient levels fall within this indeterminate range. These tests include repeat testing of plasma/urinary fractionated metanephrines and plasma catecholamines.
As a screening tool:
• Any sample in which the concentrations of both normetanephrine and metanephrine are less than upper reference range limit should be considered normal and the presence of pheochromocytoma is highly unlikely.
• Any sample where the concentrations of either normetanephrine or metanephrine exceed their respective upper reference range limit should be considered elevated.
• Whenever the normetanephrine or metanephrine concentration exceeds the indeterminate range, the presence of pheochromocytoma is highly probable and should be located via imaging techniques.
There are instances in which this assay will yield false-positive results. Whenever the results of normetanephrine and/or metanephrine are within, but neither result exceeds, the indeterminate range, follow-up biochemical testing is suggested according to the Pheochromocytoma Diagnosis Decision Tree (Related Documents, adapted from NIH).
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.
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).
|Order Code||Order Code Name||Order Loinc||Result Code||Result Code Name||UofM||Result LOINC|
|121806||Metanephrines, Frac., Pl. Free||070013||Normetanephrine, Pl||pg/mL||2669-0|
|121806||Metanephrines, Frac., Pl. Free||070023||Metanephrine, Pl||pg/mL||38494-1|