Urine metanephrine testing is primarily used to help detect and rule out pheochromocytomas in symptomatic patients. It may also be ordered to help monitor the effectiveness of treatment when a pheochromocytoma is discovered and removed and to monitor for recurrence. Urine metanephrine testing may be ordered by itself or along with a plasma metanephrine test. Plasma and urine catecholamine testing also may be ordered, either along with urine metanephrines or as follow-up tests. Since catecholamine 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, there will be a certain number of false positives. For this reason, metanephrine testing is not recommended as a screen for the general public. Doctors will frequently investigate a positive result by evaluating a patient’s stresses and intake, work to alter or minimize these influences, and then repeat the test to confirm the original findings.

Occasionally, metanephrine 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 patient 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 a patient has a pheochromocytoma or wants to rule out the possibility. He may order it when a patient has persistent or recurring hypertension along with symptoms such as headaches, sweating, flushing, and rapid heart rate. It may also be ordered when a patient has hypertension that is not responding to treatment (patients with a pheochromocytoma are frequently resistant to conventional therapies).

Occasionally, the test may be ordered when an adrenal tumor is detected incidentally or when a patient has a family history of pheochromocytomas. It also may be used as a monitoring tool when a patient has been treated for a previous pheochromocytoma.

Because the metanephrine 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 patient has large amounts of metanephrines 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 metanephrine and/or urine or plasma catecholamine testing to help confirm the findings. If these are also elevated, then imaging tests (such as an MRI) may be ordered to help find the tumor(s). If an asymptomatic patient with a tumor that has been discovered during a scan for another reason has significantly elevated metanephrines, then it is likely that the tumor discovered is a pheochromocytoma.

Serious illnesses and stresses can cause moderate to large temporary increases in metanephrine levels. Doctors must evaluate the patient 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 patient 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 patient has a pheochromocytoma.

If levels are elevated in a patient 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, however, is relatively good. This means that if the concentrations of the metanephrines are normal, then it is much less likely that the patient has a pheochromocytoma.

While metanephrine testing can help detect and diagnose pheochromocytomas, it cannot tell the doctor how big the tumor is (even small tumors can produce large amounts of catecholamines), where the tumor is (although the majority are found in the adrenal gland and most of the rest are found within the abdominal cavity), or how many tumors are present (although it is usually just one). It also cannot tell the doctor whether or not the tumor(s) are benign (although most are).

It is very important to talk to your doctor before discontinuing any prescribed medications. He will work with you to identify interfering substances and drug treatments to determine which of them can be safely interrupted and which must be continued for your 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 metanephrine testing will be different from patient to patient and are often not predictable.