Renin
Alternative names:
plasma renin activity; PRA; random plasma renin
How the test is performed:
Adult or child:
Blood is drawn from a vein (venipuncture), usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and a tourniquet (an elastic band) or blood pressure cuff is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the tourniquet to distend (fill 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 tourniquet 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.
Infant or young child:
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. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding.
How to prepare for the test:
The 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 physical and psychological preparation you can provide for this or any test or procedure depends on your child's age, interests, previous experience, and level of trust. For specific information regarding how you can prepare your child, see the following topics as they correspond to your child's age:
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:
Plasma renin activity (PRA) is measured as part of the diagnosis and treatment of hypertension.
Patients with primary hyperaldosteronism will have an increased aldosterone (for more information see the aldosterone test) production associated with a decreased PRA. Patients with secondary hyperaldosteronism (that is, caused by renal disease or renal vascular disease) will have increased plasma levels of renin and aldosterone.
Renin is an enzyme released by specialized cells of the kidney into the blood in response to sodium depletion and/or low blood volume. Renin converts angiotensinogen (a protein released into the blood by the liver) to angiotensin I. 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.
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