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ADH
Definition ADH is a test that measures the amount of ADH in serum. ADH is a hormone found in the body. It may also be given as a medication. Alternative Names Arginine vasopressin; Antidiuretic hormone; AVP; Vasopressin How the test is performed Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic. An elastic band is placed around the upper arm to apply pressure and cause the vein to swell with blood. A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the band is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding. For infants or young children: The area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. A bandage may be applied to the puncture site if there is any bleeding. How to prepare for the test Consult your health care provider about your medications before the test. Many medications, including nicotine, insulin, diuretics, lithium, morphine, alcohol, steroids, haloperidol, and clonidine can affect ADH measurements. How the test will feel When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing. Why the test is performed This test is performed if a disorder that affects the ADH level is suspected. ADH is a hormone stored in the posterior pituitary gland in the brain. It is the primary regulator of water in the body. ADH acts on the kidneys to increase total body water. This decreases the plasma concentration, increasing blood volume and increasing blood pressure. The release of ADH is controlled by cells, called osmoreceptors and baroreceptors. Osmoreceptors are specialized areas in the hypothalamus (an area in the brain). These cells sense the concentration of particles in the blood. When the concentration is high, the pituitary releases more ADH. This stimulates retention of water to dilute the body fluids. When the concentration is low, the pituitary releases less ADH. Baroreceptors are specialized areas in the heart that sense blood volume and blood pressure. The heart signals the pituitary to release more ADH when blood volume or blood pressure are low and less when they are high. In certain diseases, the normal release of ADH is altered, and the serum level of ADH must be tested to determine the cause. ADH may be measured as part of a "water restriction test" to more thoroughly investigate the cause of a disease. Normal Values Values of 0 to 4.7 pg/mL are normal. Normal value ranges may vary slightly among different laboratories. Note: pg/ml = picograms per milliliter What abnormal results mean Higher-than-normal levels may indicate: - Acute porphyria (very rare)
- Central nervous system infection
- Central nervous system tumor
- Post-surgery fluid imbalance
- SIADH (syndrome of inappropriate ADH)
- Pulmonary infections
- Pulmonary or mediastinal tumors
Lower-than-normal levels may indicate: - Damage to the pituitary gland
- Diabetes insipidus -- central or nephrogenic
- Primary polydipsia
What the risks are - Excessive bleeding
- Fainting or feeling lightheaded
- Hematoma (blood accumulating under the skin)
- Infection (a slight risk any time the skin is broken)
- Multiple punctures to locate veins
Special considerations There are none. Review date: 3/8/2006 Reviewed By: Robert Hurd, M.D., Department of Biology, College of Arts and Sciences, Xavier University, Cincinnati, OH. Review provided by VeriMed Healthcare Network.
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