Renin Assay

A renin assay blood test is done to find the cause of high blood pressure (hypertension). Renin is an enzyme made by special cells in the kidneys. Renin works with aldosterone (a hormone made by the adrenal glands) and several other substances to help balance sodium and potassium levels in the blood and fluid levels in the body, which affects your blood pressure.

A renin test is often done at the same time as an aldosterone test. In some people, it may be normal to have high blood levels of both renin and aldosterone. If renin levels are low and aldosterone levels are high, a tumor may be present in the adrenal glands.

A renin test is done to find the cause of high blood pressure (hypertension), especially when potassium levels in the blood are low.

For 2 to 4 weeks before the test, you will be asked to stop taking medicines that can affect the test, such as diuretics, estrogens, and high blood pressure medicines (especially beta-blockers and ACE inhibitors). Your health professional may have you take other medicines for a few weeks that will not change the renin test results.

Do not eat natural black licorice for 2 weeks before the test. Do not eat or drink foods that contain caffeine the day before the test. Natural licorice and caffeine can change the test results.

For 3 days before a renin test, you may be asked to follow a special low-sodium diet.

You will be asked to not eat or drink anything for 8 hours before the test.

You may need to sit or lie down to relax for 1 to 2 hours before your blood is collected. A second blood sample may be collected after you move around for 2 hours.

The health professional drawing blood will:

• Wrap an elastic band around your upper arm to stop the flow of blood. This makes the veins below the band larger so it is easier to put a needle into the vein.
• Clean the needle site with alcohol.
• Put the needle into the vein. More than one needle stick may be needed.
• Attach a tube to the needle to fill it with blood.
• Remove the band from your arm when enough blood is collected.
• Put a gauze pad or cotton ball over the needle site as the needle is removed.
• Put pressure to the site and then a bandage.

The blood sample is taken from a vein in your arm. An elastic band is wrapped around your upper arm. It may feel tight. You may feel nothing at all from the needle, or you may feel a quick sting or pinch.

There is very little chance of a problem from having blood sample taken from a vein.

• You may get a small bruise at the site. You can lower the chance of bruising by keeping pressure on the site for several minutes.
• In rare cases, the vein may become swollen after the blood sample is taken. This problem is called phlebitis. A warm compress can be used several times a day to treat this.
• Ongoing bleeding can be a problem for people with bleeding disorders. Aspirin, warfarin (Coumadin), and other blood-thinning medicines can make bleeding more likely. If you have bleeding or clotting problems, or if you take blood-thinning medicine, tell your doctor before your blood sample is taken.

A renin assay blood test is done to find the cause of high blood pressure (hypertension). The time of day and your position (standing, sitting, or lying down) before the blood sample is collected, your age, and the level of sodium in your blood all affect the test results.

Normal

Normal values may vary from lab to lab.

High values

A high renin value can mean kidney disease, blockage of an artery leading to a kidney, Addison's disease, cirrhosis, excessive bleeding (hemorrhage), or malignant high blood pressure is present.

Low values

A low renin value can mean Conn's syndrome is present.

Reasons you may not be able to have the test or why the results may not be helpful include:

• Eating natural black licorice in the 2 weeks before the test.
• Taking some medicines used to treat high blood pressure.
• Taking aspirin, caffeine, estrogens, or diuretics.
• Your position (standing, sitting, or lying down) before the test is done or the time of day when the blood sample is drawn, as well as recent salt intake.
• Taking very high doses of corticosteroids.
• Being pregnant.

• Many factors can affect renin test results. Your doctor will talk with you about any abnormal results that may be related to your symptoms and medical history.
• A renin test is often done at the same time as an aldosterone test. For more information, see the medical test Aldosterone.
• A renin stimulation test may occasionally be done if blood renin levels are low. To prepare for this test, you will eat a low-sodium diet for 3 days. A blood renin level will be drawn and a diuretic, usually furosemide (Lasix), will be put in a vein (intravenous) in your arm. Normally, blood renin levels will increase, but in Conn's syndrome blood renin levels will not change after taking the diuretic.
• Many hospitals now measure renin activity with the renin direct immunoassay, which measures the amount of renin in the blood. A plasma renin activity (PRA) test measures an enzyme called angiotensin I rather than renin itself. A renin direct immunoassay is easier to do and can generally be done instead of the PRA test. However, in some situations (such as pregnancy), PRA results may be more accurate than the renin direct immunoassay.
• If a kidney artery is blocked, another test, such as a captopril test, may be done. For the captopril test, you will take a dose of captopril after the renin assay test is done and your blood pressure is measured. Follow-up blood pressure measurements and a PRA test are done 60 minutes later to find high blood pressure. Other tests that may also be done are duplex Doppler ultrasound or arteriography. For more information, see the medical tests Doppler Ultrasound and Angiogram.

Other Works Consulted

• Chernecky CC, Berger BJ, eds. (2004). Laboratory Tests and Diagnostic Procedures, 4th ed. Philadelphia: Saunders.

• Fischbach FT, Dunning MB III, eds. (2004). Manual of Laboratory and Diagnostic Tests, 7th ed. Philadelphia: Lippincott Williams and Wilkins.

• Pagana KD, Pagana TJ (2006). Mosby’s Manual of Diagnostic and Laboratory Tests, 3rd ed. St. Louis: Mosby.