24h urine collection
Please note Capsaicin contained in chillies can cause an interference in our assay. Patients should avoid any meals containing chillies for a minimum of 48 hours prior to collecting the 24h urine sample. Drug interference (Rifampicin or Pyridoxine) can also cause markedly elevated normetanephrines.
|Normetaneprhine||Males||up to 5.3 umol/24H|
|Females||up to 4.3 umol/24H|
|Metanephrine||All||up to 2.0 umol/24H|
Phaeochromocytoma is a tumour arising from the chromaffin cells of the adrenal medulla. Phaeochromocytoma and other tumours derived from neural crest cells, such as paragangliomas and neuroblastomas, secrete the catecholamines, adrenaline and noradrenaline. The ratio of adrenaline to noradrenaline is normally 0.2. Noradrenaline is synthesized from tyrosine via dopa and dopamine in the brain, chromaffin tissue, and sympathetic nerve endings. Adrenaline is formed from noradrenaline in adrenal chromaffin cells. Both compounds are inactivated by catechol-O-methyl transferase to form normetadrenaline and metadrenaline. Plasma metadrenalines exist as free (< 7%) and conjugated (93%) forms. Some normetadrenaline and metadrenaline is converted to vanillylmandelic acid (VMA). Urine contains small amounts of catecholamines and much larger amounts of metadrenaline, normetadrenaline, and VMA.
Phaeochromocytomas occur in about one of every 1000 hypertensive patients; about half of those affected have paroxysmal hypertension. They occur equally in men and women, primarily during the third through fifth decades of life. Symptoms are dependent on the quantity of catecholamine secreted and whether the release is sustained or intermittent. Most tumours usually secrete more noradrenaline than adrenaline. Patients typically present with dramatic paroxysms of hypertension accompanied by severe headache, pallor, drenching perspiration, and palpitations. Paroxysms may occur anywhere from once a year to several times a day and usually persist for 10 to 60 minute’s duration.
The biochemical diagnosis of phaeochromocytoma depends on the demonstration of excessive production of these hormones. Measurement of metanephrines is more sensitive than measurement of catecholamines because they are more stable. For routine screening purposes the RDE is currently offering urine total fractionated urinary metanephrines to replace urine catecholamines which are inferior in terms of sensitivity and specificity.
In some circumstances, we can arrange for plasma free fractionated metadrenalines. The high sensitivity of plasma free or urinary fractionated metanephrines means that normal test results almost always exclude the presence of phaeochromocytoma. Exceptions include asymptomatic small tumors that produce and metabolize negligible amounts of noradrenaline or adrenaline. Also, patients being treated with metyrosine may have artifactually decreased plasma metadrenaline levels.
Elevated metadrenaline levels do not always indicate phaeochromocytoma. Elevated results may be caused by physical stress or medications. Many of the patients being tested for phaeochromocytoma have underlying clinical conditions that are associated with increased sympathetic activity such as hypertension, heart failure, stroke, baroreflex failure and cardiogenic shock.
Substances that increase endogenous catecholamine levels can result in borderline elevations of plasma metadrenalines. Examples include:
1. Peaston RT and Lai LC. Biochemical detection of phaeochromocytoma; Should we still be measuring urinary HMMA?. J Clin Path 1993; 468:734-7.
2. Peaston RT, Lennard TWJ, Lai LC. Overnight excretion of urinary catecholamines and metabolites in the detection of phaeochromocytoma. J Clin Endocrin Metab 1995; 81:1378-84.
3. Parker NC, Letvtzow CB, Wright PW et al. Uniform chromatographic conditions for quantifying urinary catecholamines and metadrenalines. Clin Chem 1986;32:1473-76.
Cannot be added on to an existing requestSpecimen Labelling Procedure