Test Overview

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.

Why It Is Done

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

How To Prepare

For 2 to 4 weeks before the test, you may 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 doctor 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 may be asked to not eat or drink anything for 8 hours before the test.

How It Is Done

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.

A health professional uses a needle to take a blood sample, usually from the arm.

How It Feels

When a blood sample is taken, you may feel nothing at all from the needle. Or you might feel a quick sting or pinch.

Risks

There is very little chance of having a problem from this test. When a blood sample is taken, a small bruise may form at the site.

Results

Normal

Each lab has a different range for what's normal. Your lab report should show the range that your lab uses for each test. The normal range is just a guide. Your doctor will also look at your results based on your age, health, and other factors. A value that isn't in the normal range may still be normal for you.

High values

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

Low values

A low renin value can mean that some types of kidney disease or Conn's syndrome is present.