24-hour urinary metanephrines
This test measures the amount of metanephrines in your urine that your body produces over a 24-hour period.
Metanephrines are a byproduct of the breakdown of hormones called catecholamines, which are made by the adrenal glands. Catecholamines are responsible for the body's response to stress. They are sometimes called "fight or flight" hormones and also include epinephrine, norepinephrine, and dopamine.
You may need this test if your doctor suspects you have a condition called pheochromocytoma or paraganglioma. These are rare tumors that produce excess amounts of catecholamines. Pheochromocytomas are found in the adrenal glands, and paragangliomas are found outside the adrenal glands.
Signs and symptoms of pheochromocytoma or paraganglioma include:
High blood pressure
Your doctor may also order a blood test that measures metanephrines, called a fractionated plasma metanephrine test. Other byproducts of catecholamines may also be measured.
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.
Total urinary metanephrines can be measured in milligrams (mg). A level of 1.3 mg or greater over 24 hours is often considered positive.
Different laboratories have different ways of measuring catecholamine levels. Your doctor will discuss your results with you.
If your 24-hour metanephrine level is between one and two times the normal amount, there is about a 30 percent chance you have a pheochromocytoma or paraganglioma.
If your 24-hour metanephrine level is twice the normal level or higher, it's likely that you have a pheochromocytoma or paraganglioma. You may need to have imaging tests, including CT or MRI scans. These tests are done to confirm the diagnosis and locate the tumor.
This test requires a 24-hour urine sample. For this type of urine sample, you must collect all the urine you produce for 24 hours. Empty your bladder completely first thing in the morning without collecting it and note the time. Then collect your urine every time you go to the bathroom for the next 24 hours.
Your health care provider will probably give you specific instructions. Follow them carefully.
This test poses no known risks.
Certain medications, foods, and conditions can cause metanephrine and catecholamine levels to be higher than normal. These include:
Antidepressants and amphetamines
Physical or emotional stress
Withdrawal from drugs or alcohol
Obstructive sleep apnea
Don't drink anything containing caffeine before or during the test. Tell your doctor if you are taking medication, and ask whether you have any food, medication, or activity restrictions. Be sure your doctor knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illicit drugs you may use.
Plan to be home for the 24 hours you do the test so you can store the urine sample properly.