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Alternative namesPlasma renin activity; Random plasma renin; PRA
DefinitionThe renin test measures the amount of renin in the blood.
How the test is performed
Adult or child:
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.
How to prepare for the testThe health care provider may advise you to withhold drugs that can affect the test (see "Special considerations").
Consume a normal, balanced diet with low-sodium content (about 3 gm/day) for 3 days before the test.
Infants and children:
The preparation you can provide for this test depends on your child's age, previous experiences, and level of trust. For general information regarding how you can prepare your child, see the following topics:
How the test will feelWhen 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
Plasma renin activity (PRA) is measured as part of the diagnosis and treatment of hypertension .
Patients may also have renin and aldosterone levels checked in essential hypertension to evaluate if patients are salt-sensitive. This will cause a low renin with normal aldosterone levels, and this helps to guide the physician in choosing the correct medication for these patients. Salt-sensitive patients with low renin hypertension respond well to diuretic medications.
Angiotensin I is converted to angiotensin II by an enzyme in the veins of the lungs. Angiotensin II acts on the adrenal cortex to stimulate the release of aldosterone. Aldosterone acts on the distal tubules of the kidneys to decrease the loss of sodium ions and secondarily fluid. This has the effect of increasing blood pressure. In addition, angiotensin causes constriction of small blood vessels, which also increases blood pressure.
Normal ValuesNormal values range from 1.9 to 3.7 ng/ml/hour. Normal value ranges may vary slightly among different laboratories.
Note: ng/ml/hour = nanograms per milliliter per hour
What abnormal results mean
Abnormal results are indicated as follows:
Greater-than-normal levels may indicate:
What the risks are
Special considerationsRenin measurements are affected by pregnancy, salt intake, time of day, and a standing vs. prone position.
Drugs that can affect renin measurements include antihypertensives, diuretics, estrogens, oral contraceptives, and vasodilators.
Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.
Update Date: 2/11/2004Irfan A. Agha, M.D., Department of Medicine, Renal Division, St. Louis University, St. Louis, MO. Review provided by VeriMed Healthcare Network.
Last updated: Tue, 06 Jan 2009 00:20:03 GMT