Urine metanephrines testing is primarily used to help detect and rule out pheochromocytomas in symptomatic people. It may also be ordered to help monitor the effectiveness of treatment when a pheochromocytoma is removed to monitor for recurrence. Urine metanephrines testing may be ordered by itself or along with a plasma metanephrines test. Plasma and urine catecholamines testing may also be ordered, either along with urine metanephrines or as follow-up tests. Since catecholamines secretion tends to fluctuate over time, a 24-hour urine test for metanephrines or catecholamines may detect excess production that is missed with the blood test. It is up to the doctor to decide which test or test combinations will give him the most information. In many cases, urine and plasma metanephrines may be preferred as they are usually present in greater quantities than catecholamines in the urine and can persist in the blood even when catecholamine levels have returned to normal.
Since these tests are affected by drugs, foods, and stresses, false positive tests may occur. For this reason, metanephrines testing is not recommended as a screen for the general public. Doctors will frequently investigate a positive result by evaluating a person's stress, diet, and medications, work to alter or minimize these influences, and then repeat the test to confirm the original findings.
Occasionally, metanephrines testing may be ordered on an asymptomatic person if an adrenal or neuroendocrine tumor is detected during a scan that is done for another purpose or if the person has a strong personal or family history of pheochromocytomas (as they may recur and there is a genetic link in some cases).
Urine metanephrines are ordered when a doctor either suspects that someone has a pheochromocytoma or wants to rule out the possibility. He may order it when a person has persistent or recurring hypertension along with symptoms such as headaches, sweating, flushing, and rapid heart rate. It may also be ordered when a person has hypertension that is not responding to treatment. Since the hormone production from a pheochromocytoma is not regulated by the body, those who have hypertension due to a pheochromocytoma are frequently resistant to conventional therapies.
Occasionally, the test may be ordered when an adrenal tumor is detected incidentally or when someone has a family history of pheochromocytomas. It also may be used as a monitoring tool when a person has been treated for a previous pheochromocytoma.
Because the urine metanephrines test is sensitive to many outside influences and pheochromocytomas are rare, a doctor may see more false positives with this test than true positives. If a symptomatic person has large amounts of metanephrine and/or normetanephrine in his urine, further investigation is indicated. If there are no interfering substances or stresses identified, then there is a good possibility that he may have a pheochromocytoma. The doctor may order plasma metanephrines and/or urine or plasma catecholamines testing to help confirm the initial findings. If these are also elevated, then imaging tests such as an MRI may be ordered to help locate the tumor(s).
Serious illnesses and stresses can cause moderate to large temporary increases in metanephrines levels. Doctors must evaluate the person as a whole – his physical condition, emotional state, medications, and diet. When interfering substances and/or conditions are found and resolved, the doctor will frequently re-test the person to determine whether the metanephrines are still elevated. If they are, then he may order imaging scans; if they are not, then it is unlikely that the person has a pheochromocytoma.
If levels are elevated in someone who has had a previous pheochromocytoma, it is likely that either treatment was not fully effective or that the tumor is recurring.
The negative predictive value of the test is relatively good. This means that if metanephrine and normetanephrine concentrations are normal, then it is unlikely that a person has a pheochromocytoma.
While metanephrines testing can help detect and diagnose pheochromocytomas, it cannot tell the doctor how big the tumor is, where it is, how many tumors are present, or whether or not the tumor(s) are benign – although most are. Even small tumors can produce large amounts of catecholamines.
It is very important to talk to the doctor before discontinuing any prescribed medications. He will work with the person being tested to identify interfering substances and drug treatments to determine which of them can be safely interrupted and which must be continued for a person's well-being. Some of the substances that can interfere with metanephrine testing include: acetaminophen, aminophylline, amphetamines, appetite suppressants, coffee, tea, and other forms of caffeine, chloral hydrate, clonidine, dexamethasone, diuretics, epinephrine, ethanol (alcohol), insulin, imipramine, lithium, methyldopa (Aldomet), MAO (monoamine oxidase) inhibitors, nicotine, nitroglycerine, nose drops, propafenone (Rythmol), reserpine, salicylates, theophylline, tetracycline, tricyclic antidepressants, and vasodilators. The effects of these drugs on metanephrines testing will be different from person to person and are often not predictable.
This article was last reviewed on February 24, 2012. | This article was last modified on February 26, 2013.
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