Adrenomedullary Hormone Tests Health Article

Definition

Adrenomedullary hormone tests measure levels of the hormones epinephrine, norepinephrine, and dopamine found in blood and urine. This group of tests also includes urine tests for the catabolic products (break-down products) of these hormones, known alternately as metabolites. Epinephrine, norepinephrine, and dopamine, collectively called catecholamines, are manufactured by chromaffin cells in the medulla (center) of the adrenal glands and are derived from the amino acid tyrosine. They help ready the body for the "fight-or-flight" response, also known as the alarm reaction. When adrenomedullary hormones are released at times of stress, the heart beats stronger and faster, blood pressure rises, blood flow is increased to the brain and muscles, and the liver releases glucose (sugar) as energy the body can readily use. Simultaneously, the rate of breathing increases, airways in the respiratory system widen, and digestive activity slows. These reactions quickly direct more oxygen and fuel to the brain, heart, and skeletal muscles, the organs most active in responding to stress.

The adrenomedullary hormone tests (also called catecholamines, dopamine, norepinephrine, epinephrine, or adrenalin tests) may be performed on blood or urine specimens. Urine tests are also used to measure the metabolites vanillylmandelic acid (VMA), metanephrine and normetanephrine, and homovanillic acid (HVA). Catecholamines are released from the adrenal gland in pulses causing blood levels to be quite variable. Measurements of catecholamines and their metabolites in 24-hour urine samples are generally preferred because they are not subject to pulse variation.

Purpose

Only small amounts of adrenomedullary hormones are found in the urine of healthy people. Excessive levels may be secreted in conditions that affect hormone production, such as pheochromocytoma (a tumor of the chromaffin cells of the adrenal gland) and rare tumors of the nervous system (neuroblastomas, ganglioneuroblastomas, and ganglioneuromas). Elevated hormone levels often result in constant or intermittent high blood pressure (hypertension). Episodes of high blood pressure may be accompanied by symptoms such as headache, sweating, palpitations, and anxiety. The adrenomedulary hormone test can be ordered to help determine if high blood pressure is related to abnormal hormone secretion and to either exclude a tumor as the underlying cause or to identify the type of tumor that may be increasing hormone levels.

Description

Adrenomedullary hormone tests are typically performed by medical technologists in the clinical laboratory on either blood plasma or 24-hour urine samples. If performed on blood, the test may require drawing one or two samples, depending on the physician's request. The objective may be to measure changes in adrenomedullary hormone production over a specific time period or in certain conditions, such as changes in temperature, posture, diet, or medications. The first blood sample will usually be drawn after the patient has been lying down in a warm, comfortable environment for at least 30 minutes. If a second sample is needed, the patient will be asked to stand for 10 minutes before the blood is drawn. Instead of a venipuncture, which can be stressful for the patient and can actually increase adrenomedullary hormone levels in the blood, a catheter (a small plastic tube-like device) may be inserted in a vein 24 hours in advance. This allows the blood sample to be collected without the stress of needle puncture at the time of the test.

Because blood levels of adrenomedullary hormones commonly go up and down in response to factors such as temperature, stress, postural change, diet, smoking, obesity, and certain drugs, abnormally high blood levels should be confirmed with a 24-hour urine test. It is also important to consider that hormone secretion from a tumor may not be steady, but may occur periodically during the day. Consequently, an elevation in hormone levels potentially could be missed if only the blood test is performed. By contrast, the urine test requires that all urine passed during a 24-hour period must be collected by the patient or a healthcare professional, ensuring that the urine specimen reflects hormone production over an entire day.

The recommended procedure for measuring catecholamines and their metabolites is chromatography. High-performance liquid chromatography with electro-chemical detection (HPLC-EDC) or liquid chromatography with mass spectrometry detection (LC-MS) are both sensitive and specific and have the advantage of being able to measure epinephrine, norepinephrine, and dopamine simultaneously. HPLC-EDC is also the method of choice for simultaneous measurement of VMA and HVA, although this procedure requires different extraction and separation conditions than are used for catecholamines. VMA can also be measured by a column-diazo method that is free of interference from dietary vanillin. The VMA is extracted from the urine and isolated on a silica gel column. The column is washed to remove interfering substances and the VMA is eluted and reacted with a diazonium salt to form a purple colored complex. Metanephrines are most often measured by HPLC-EDC or by gas chromatography-mass spectrometry. Immunoassay and radioenzymatic assays are also used for the measurement of catecholamines and metanephrines. These methods require enzymatic conversion to a derivative before measuring the catecholamine or metabolite.