Adrenomedullary Hormone Tests
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.
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
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.
There are no notable precautions with either blood or urine tests for adrenomedullary hormones. Physicians will determine if restrictions for the tests are appropriate for patients being treated with medications for high blood pressure or heart disease. When blood is used, universal precautions should be followed for the prevention of transmission of bloodborne pathogens.
Physicians will instruct patients to discontinue use of certain medications for up to two weeks before the test or will write orders to this effect for patients in nursing facilities. Drugs that may increase catecholamine levels include caffeine, nicotine, levodopa, lithium, amino-phylline, clonidine, erthromycin, insulin, methyldopa, tetracyclines, and nitroglycerin. Drugs that may decrease catecholamine levels include clonidine, imipramine, MAO inhibitors, phenothiazines, salicylates, and reserpine. The patient should fast (nothing to eat or drink) for 10 to 24 hours before the blood test and should cease smoking for 24 hours before testing. Other restrictions may be required either by individual physicians or by the laboratory, depending on the tests requested. Vigorous physical exercise and emotional stress should be avoided before the test to prevent alteration of test results by increasing secretions of epinephrine and norepinephrine.
The clinical laboratory will provide instructions and containers for patients collecting their own 24-hour urine samples. Catecholamines and their metabolites are rapidly degraded above pH 2.0. Therefore, 10 mL of 6N hydrochloric acid or concentrated sulfuric acid will be present in the container. Patients should be advised to avoid touching the preservative in the collection container. If the preservative comes in contact with the skin, the area should be rinsed with water immediately. Collection should begin in the morning on any day except Friday or Saturday to ensure that samples will be delivered to the laboratory on a work day. Urine samples must be refrigerated continuously in the patient's home or in the nursing
Following venipuncture for blood plasma hormone tests, the laboratory technologist, nurse, or phlebotomist drawing the sample should inspect the venipuncture site to make sure that the wound has closed and no bleeding is present. The site should be covered with an adhesive bandage. There is no notable aftercare for patients under-going 24-hour urine hormone tests. Patients can be reminded to resume foods and medications that were restricted prior to testing.
Complications from drawing blood are minimal and may include slight bleeding from the venipuncture site, fainting, or lightheadedness after the blood sample is drawn. Blood may accumulate under the puncture site (hematoma) if pressure is not applied to the site immediately after drawing blood. There are no complications for the urine test, although patients must avoid touching the preservative in the collection containers.
Reference ranges are laboratory-specific and vary with age and according to the test methodology used. Normal values for blood and urine tests are different. High performance liquid chromatography (HPLC) is the most common test method. Other methods especially spectophotometric and fluorometric determinations are less specific and give higher results. Urinary levels are influenced by renal function and it has become customary to report urinary catecholamines and their metabolites per gram of creatinine excreted especially when a random urine is used. Typical adult values for HPLC blood and urine tests follow.
Reference ranges for blood plasma hormone levels:
- Supine (lying down): Epinephrine less than 50 picograms per milliliter (pg/mL), norepinephrine less than 410 pg/mL, and dopamine less than 30 pg/mL.
- Standing: Values for blood specimens taken when the subject is standing are higher than the ranges for supine posture for epinephrine (less than 140 pg/mL) and norepinephrine (less than 1700 pg/mL), but not for dopamine.
Reference ranges for urine hormone levels:
- Epinephrine: 0.5 to 20 micrograms per 24 hours (mcg/24 hrs) or 0 to 20 micrograms per gram creatinine.
- Norepinephrine: 15 to 80 mcg/24 hrs or 0-45 mcg per gram creatinine.
- HVA: 65 to 400 mcg/24 hrs or 0 to 8 mg per gram creatinine.
- Total catecholamines: 14 to 110 mcg/24 hrs.
- VMA: 2 to 7 milligrams(mg)/24 hrs or 0 to 6 mg per gram creatinine.
- Metanephrine: 24 to 96 mcg/24 hrs or 0 to 300 mcg per gram creatinine.
- Normetanephrine: 75 to 375 mcg/24 hrs or 0 to 400 mcg per gram creatinine.
Elevated levels of the individual adrenomedullary hormones can indicate different conditions and/or causes, depending on which hormone or combination of hormones is elevated:
- Pheochromocytoma most commonly causes an increase in norepinephrine, metanephrines, and VMA although other catecholamines may also be increased. Measurement of 24-hour urinary metanephrines is considered the most sensitive test for this condition. When both metanephrines and VMA are used, the test approaches 100% in its clinical sensitivity. Neuroblastomas most frequently produce dopamine, norepinehprine, HVA, and VMA. HVA is the most specific marker since it is least likely to be increased in pheochromocytoma. The sensitivity with HVA alone is about 70%. The recommended initial tests for neuroblastoma includes both HVA and VMA to increase diagnostic sensitivity.
- Elevations of catecholamines and their metabolites are possible with, but do not directly confirm, thyroid disorders, low blood sugar (hypoglycemia), or heart disease.
- Electroshock therapy, or shock resulting from hemorrhage or exposure to toxins, can raise hormone levels.
- In the patient with normal or low baseline hormone levels, failure to show an increase in the sample taken after standing suggests an autonomic nervous system dys-function (the division of the nervous system responsible for the automatic or unconscious regulation of internal body functioning).
- In the absence of a tumor or other clinical findings, elevated adrenomedulary hormones may indicate prolonged stress or acute anxiety. They may also be elevated during serious physical illness.
Health care team roles
A physician orders adrenomedullary hormone tests and will typically instruct the patient about preparatory
steps required. A laboratory technologist, nurse, or a phlebotomist (someone specifically trained in venipuncture technique) will perform a venipuncture to obtain blood samples, collecting blood in a tube that contains anticoagulant. If two samples are drawn, this may take about 45 minutes. Health care providers may help encourage the patient to remain quiet and calm prior to the test and between the drawing of samples. Laboratories will provide containers for urine collection and should help ensure compliance by providing written instructions for 24-hour urine collection. Laboratory technologists or nursing staff interacting with the patient may gently question the patient at the time of the blood test or urine collection about fasting or about having discontinued the use of caffeine, nicotine, prohibited foods and medications prior to the test. Testing is performed by a clinical laboratory scientist/medical technologist.
Because tests for adrenomedullary hormones are especially sensitive, patient compliance with restrictions is essential. It is important for outpatients undergoing the adrenomedullary hormone tests to receive written instructions regarding dietary restrictions, changes in medications, and instructions for 24-hour urine collection. These instructions can be prepared by the laboratory and supplied to physicians and nursing units in health care facilities. Urine collection instructions should be written in a step-wise manner. Laboratory and nursing staff can explain each step, reminding the patient to refrigerate the urine at all times and deliver the container to the laboratory promptly at the end of the 24-hour period. Health care providers should also encourage the patient to drink clear fluids regularly throughout the urine collection process.
Laboratory technologists performing adrenomedullary hormone tests will have undergone education and training in biochemistry, enabling them to understand the role of these hormones in the body and the chemical basis for expression of the hormones in body fluids. Hands-on clinical laboratory training will prepare technologists to perform HPLC or other methods of measuring adrenomedullary hormones in blood and urine. Nursing personnel responsible for patients undergoing testing for
Catabolic—Catabolism and catabolic refer to the breakdown of complex substances in the body into simpler ones, which are called catabolic products.
Catecholamines—A collective term for the major adrenomedullary hormones epinephrine, norepinephrine, and dopamine. Catecholamines are known to be elevated in the presence of certain tumors, in severe stress, strenuous exercise, acute anxiety, and serious illness.
Dopamine—A precursor of epinephrine and norepinephrine. It is a neurotransmitter (transmits impulses between cells) primarily found in the brain.
Epinephrine—Also called adrenalin, is a naturally occurring hormone released by the medulla of the adrenal glands in response to signals from the sympathetic nervous system. These signals are triggered by stress, exercise, or by emotions such as fear.
Ganglioneuroma—A tumor composed of mature nerve cells.
Homovanillic acid (HVA)—A catabolic product or metabolite of the major adrenomedullary hormone dopamine.
Metanephrine—A catabolic product or metabolite of the adrenomedullary hormones epinephrine and norepinephrine.
Neuroblastoma—A rare tumor of the adrenal glands or sympathetic nervous system. Neuroblastomas can range from being benign (relatively harmless) to malignant.
Norepinephrine—A hormone secreted by nerve endings of the sympathetic nervous system and by the adrenal medulla. It is a neurotransmitter whose primary function is to help maintain constant blood pressure by stimulating certain blood vessels to constrict when blood pressure falls below normal.
Normetanephrine—A catabolic product or metabolite of the adrenomedullary hormone norepinephrine and epinephrine.
Pheochromocytoma—A tumor that originates from the overproduction of powerful adrenomedullary hormones by the chromaffin cells of the adrenal glands.
Vanillylmandellic acid—A product of catabolism of the adrenomedullary hormones metanephrine and normetanephrine.
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L. Lee Culvert