What is being tested?Catecholamines are a group of similar
hormones produced in the medulla (central portion) of the adrenal glands. The adrenal glands are small, triangular organs located on top of each kidney. The primary catecholamines are dopamine, epinephrine (adrenaline), and norepinephrine. These hormones are released into the bloodstream in response to physical or emotional stress. They help transmit nerve impulses in the brain, increase glucose and fatty acid release (for energy), dilate bronchioles (small air passages in the lungs), and dilate the pupils. Norepinephrine also constricts blood vessels (increasing blood pressure) and epinephrine increases heart rate and
metabolism. After completing their actions, the hormones are metabolized to form inactive compounds. Dopamine becomes homovanillic acid (HVA), norepinephrine breaks down into normetanephrine and vanillylmandelic acid (VMA), and epinephrine becomes metanephrine and VMA. Both the hormones and their
metabolites are excreted in the urine.
Normally, catecholamines and their metabolites are present in the body in small, fluctuating amounts that only increase appreciably during and shortly after a bout of stress. Pheochromocytomas and other neuroendocrine tumors, however, can produce large amounts of catecholamines, resulting in greatly increased concentrations of the hormones and their metabolites in both the blood and urine. This can cause persistent hypertension (high blood pressure) and/or bouts or episodes of severe hypertension, resulting in symptoms such as severe headaches, palpitations, sweating, nausea, anxiety, and tingling in the extremities.
About 90% of pheochromocytomas are located in the adrenal glands. While a few are cancerous, most are benign - they do not spread beyond their original location - although most do continue to grow. Left untreated, the symptoms may worsen as the tumor grows and, over a period of time, the hypertension that the pheochromocytoma causes may damage body organs, such as the kidneys and heart, and raise the risk of an affected patient having a stroke or heart attack.
Urine and plasma catecholamine testing can be used to help detect the presence of pheochromocytomas. Although only about 800 cases a year are diagnosed in the U.S. according to the National Cancer Institute, it is important to diagnose and treat these rare tumors because they cause a potentially curable form of hypertension. In most cases, the tumors can be surgically removed and/or treated to significantly reduce the amount of catecholamines being produced and to reduce or eliminate their associated symptoms and complications.
Catecholamine testing measures the amount of epinephrine, norepinephrine, and dopamine in the plasma or urine. (The metabolites of these hormones may be measured separately with a urine metanephrine and/or VMA test). The plasma catecholamine test measures the amount of hormones present at the moment of collection, while the urine test measures the amount excreted over a 24-hour period.
How is the sample collected for testing?For the
24-hour urine collection, all of your urine should be saved for a 24-hour period. It is important that the sample be refrigerated during this time period.
Plasma catecholamines are collected by inserting a needle into a vein in your arm. Although there is some disagreement over the specifics of how the sample should be collected, you may be asked to lie down and rest quietly for 15 – 30 minutes prior to sample collection, and your blood may be collected while you are lying down. In other circumstances, you may just be seated upright with little or no rest time before the sample collection.
