Catecholamines testing is primarily used to help detect or rule out pheochromocytomas in symptomatic people. It also may be ordered when a pheochromocytoma is removed to monitor for recurrence. The blood test is most useful when the person has persistent hypertension or is currently experiencing an episode of hypertension. This is because the hormones do not linger in the blood; they are used by the body, metabolized, and/or excreted. Urine catecholamines testing measures the total amount of catecholamines released in 24 hours. Since the hormone levels may fluctuate significantly during this period, the urine test may detect excess production that is missed with the blood test. Blood and urine tests may be ordered together or separately to look for excessive amounts of both catecholamines and their metabolites.
Since these tests are affected by drugs, foods, and stresses, false positive tests can occur. For this reason, catecholamine testing is not recommended as a screen for the general public. Doctors will frequently investigate a positive result by evaluating a person's stresses, work to alter or minimize any influences, and then repeat the test to confirm the original findings.
Occasionally, the tests may be ordered on an asymptomatic person if an adrenal or neuroendocrine tumor is detected during a scan conducted for another purpose or if the person has a strong personal or family history of pheochromocytoma.
Catecholamines testing is ordered when a doctor either suspects that a person has a pheochromocytoma or wants to rule out the possibility. He may order it when someone 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 as people with pheochromocytomas 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 may also be used as a monitoring tool when a person has been treated for a previous pheochromocytoma.
Since the catecholamines 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 catecholamines in her blood and/or urine, further investigation is indicated. Serious illness and stress can cause moderate to large temporary increases in catecholamine levels. Doctors must evaluate the person as a whole - her 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 catecholamines are still elevated. The doctor may also order blood and/or urine metanephrine testing to help confirm his findings and imaging tests, such as an MRI, to help locate the tumor(s).
If catecholamine levels are elevated in a person who has had a previous pheochromocytoma, then it is likely that either treatment was not fully effective or that the tumor is recurring.
If the concentrations of catecholamines are normal in both the plasma and urine, then it is unlikely that a person has a pheochromocytoma. Pheochromocytomas do not necessarily produce catecholamines at a constant rate, however. If the person has not had a recent episode of hypertension, their blood and urine concentrations of catecholamines could be at normal or near normal levels even when a pheochromocytoma is present.
While plasma and urine catecholamines testing can help detect and diagnose pheochromocytomas, they cannot tell the doctor where the tumor is, whether there is more than one, or whether or not the tumor is benign (although most are). The amount of catecholamines produced does not necessarily correspond to the size of the tumor. This is a physical characteristic of the tumor tissue. The total amount of catecholamines produced will tend to increase, however, as the tumor increases in size.
A variety of medications can interfere with catecholamines testing. However, it is important to talk to the doctor before discontinuing any prescribed medications. He will work with the person being tested to identify potentially interfering substances and drug treatments and to determine which of them can be safely interrupted and which must be continued for the person's well-being. Some of the substances that can interfere with catecholamines 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 catecholamines results will be different from person to person and are often not predictable.
While 90% of pheochromocytomas are found in the adrenal glands, most of the remaining 10% are typically found in the abdominal cavity. The World Health Organization uses the term "extra-adrenal paraganglioma" to describe catecholamine-producing tumors that are not located in the adrenal glands.
This article was last reviewed on February 23, 2012. | This article was last modified on February 26, 2013.
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