Definition
- Metanephrine and normetanephrine are metabolic products of epinephrine and norepinephrine, the adrenal medullary hormones secreted by pheochromocytomas. Fractionated tests provide higher diagnostic sensitivity than assays for total catecholamines.
- Normal range: see Table 16.55.
TABLE 16 " 55Normal Range for Urine MetanephrinesView LargeTABLE 16 " 55Normal Range for Urine Metanephrines Age Reference Interval (mg/g Creatinine) Metanephrine " 0 " 3 mo 0 " 700 " 4 " 6 mo 0 " 650 " 7 " 11 mo 0 " 650 " 1 y 0 " 530 " 2 " 5 y 0 " 500 " 6 " 17 y 0 " 320 " ≥18 y 0 " 300 Normetanephrine " 0 " 3 mo 0 " 3,400 " 4 " 6 mo 0 " 2,200 " 7 " 11 mo 0 " 1,100 " 1 y 0 " 1,300 " 2 " 5 y 0 " 610 " 6 " 17 y 0 " 450 " ≥18 y 0 " 400
Use
- Confirmation of elevated plasma catecholamine levels
- Diagnosis of pheochromocytoma and paraganglioma
- Diagnosis and follow-up of patients with neuroblastoma and related tumors
- First line of test in patients with lower suspicion of pheochromocytoma (patients with resistant hypertension, hyper adrenergic spells, incidentally discovered adrenal mass that does not have imaging characteristics consistent with pheochromocytoma).
Interpretation
- Increases occur with catecholamine-secreting neurochromatin tumors such as pheochromocytoma, paraganglioma, and neuroblastoma.
Limitations
- No caffeine intake should occur before or during collection. MAO inhibitors should be discontinued at least 1 week prior to beginning collection.
- Methylglucamine in x-ray contrast medium can cause false-negative test results.
- False positives can be caused by stress and drugs, which includes amphetamines and amphetamine-like compounds, appetite suppressants, bromocriptine, buspirone, caffeine, carbidopa " levodopa (Sinemet), clonidine, dexamethasone, diuretics, methyldopa (Aldomet), nose drops, propafenone (Rythmol), tricyclic antidepressants, and vasodilators. The effects of some drugs on catecholamine metabolite results may not be predictable.