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Metanephrines (Blood)

Does this test have other names?

Metanephrine, plasma free

What is this test?

This test measures the substances metanephrine and normetanephrine in your blood. It helps find out whether you have a tumor of the adrenal glands called pheochromocytoma.

The adrenal glands sit on top of your kidneys. They make the hormone adrenaline and other adrenaline-like chemicals called cate­cholamines. Adrenaline regulates your blood pressure and helps you cope with stress. Metanephrine and normetanephrine are catecholamines that result when adrenaline breaks down.   

Doctors disagree on the best test for diagnosing adrenal gland tumors. Some doctors believe a urine test to measure catecholamines is better than this blood test because it has fewer false-positive results.

Why do I need this test?

You might have this test if your doctor suspects that you have an adrenal gland tumor. Symptoms include:

  • Rapid heartbeat

  • Headaches

  • Sweating

  • Rise and fall in blood pressure

You also may have fever, chest pain, stomach pain, nausea, vomiting, anxiety, tremors, heat intolerance, and weight loss.

Most pheochromocytomas are not cancerous.

What other tests might I have along with this test?

Your doctor may also order a urine test to measure catecholamines. He or she may also order these tests:

  • Glucagon stimulation test. This test requires you to be injected with the hormone glucagon. If you have an adrenal gland tumor and you are given glucagon, you may have symptoms.

  • Clonidine suppression test. This test measures adrenaline and noradrenaline, as well as metanephrines in your blood.

Your doctor may also order a CT, MRI, or other scan to look for a tumor.

What do my test results mean?

Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your health care provider.

Results are given in picograms per milliliter (pg/mL). Normal findings are:

  • Normetanephrine: 18 to 111 pg/mL

  • Metanephrine: 12 to 60 pg/mL

Higher levels of metanephrines may mean that you have an adrenal gland tumor. But false-positive results can occur.

Higher levels may also be caused by obstructive sleep apnea.

How is this test done?

The test requires a blood sample, which is drawn through a needle from a vein in your arm.

Does this test pose any risks?

Taking a blood sample with a needle carries risks that include bleeding, infection, bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight stinging sensation or pain. Afterward, the site may be slightly sore.

What might affect my test results?

Your results could be affected by:

  • Drinking caffeinated drinks or alcohol

  • Exercising vigorously

  • Being under a great deal of stress

  • Starving yourself

Certain medications can also affect your results. These include epinephrine- and norepinephrine-containing drugs, levodopa, lithium, nitroglycerin, and acetaminophen.

How do I get ready for this test?

Don't exercise vigorously or drink caffeinated beverages or alcohol before your test. Don't take acetaminophen for at least 48 hours before the test. Try to avoid stress. You may be asked to rest quietly for 15 to 30 minutes before your blood sample is collected.