What Is a Renin Test?

When you have high blood pressure, also called hypertension, finding the reason for it can help you get the right treatment. A renin test can shed light on what’s happening in your body.

Your doctor may order this kind of test if high blood pressure starts when you’re young or medication doesn’t keep it under control.

What Is Renin?

It’s an enzyme that helps control your blood pressure. It’s made by special cells in your kidneys.

When your blood pressure drops too low or your body doesn’t have enough salt, renin gets sent into your bloodstream. That triggers a chain reaction that creates a hormone called angiotensin and signals your adrenal glands to release another hormone called aldosterone.

Angiotensin makes tiny blood vessels narrower, and aldosterone tells your kidneys to hold on to salt and fluid. Both those things can raise your blood pressure. If that process gets out of balance, your blood pressure can get too high.

About the Test

Doctors usually test your levels of renin and aldosterone at the same time. They may call it a plasma renin activity test or an aldosterone-renin ratio.

A nurse will take a sample of your blood and send it to a lab. The test results will tell you if your renin and aldosterone levels are high, low, or normal. High or low levels may help explain why you have high blood pressure:

  • High renin with normal aldosterone may show that you’re sensitive to salt.
  • Low renin and high aldosterone may mean your adrenal glands aren’t working the way they should.
  • If both are high, it can be a sign that there’s a problem with your kidneys.

The results can help your doctor decide which medications or other treatments will work best for you.

What Can Affect the Test?

Your levels of renin and aldosterone are highest in the morning and can change during the day. It also can make a difference if you’re sitting up or lying down when your blood is taken.

Talk to your doctor about what to do before the test to make sure the results are right. A few things can throw off a renin test:

  • Medications: You may need to stop taking certain high blood pressure medicines, diuretics, hormones, steroids, or some over-the-counter painkillers for a while. Make sure your doctor knows all the drugs and supplements you take.
  • Salt: Your doctor may have you cut back on the amount you eat for several days.
  • Stress
  • Pregnancy
  • Exercise or other physical activity
  • Severe illness: You shouldn’t have the test done if you’re very sick, because your aldosterone level may be unusually low.

WebMD Medical Reference Reviewed by James Beckerman, MD, FACC on May 5, 2017

Sources

SOURCES:

American Association for Clinical Chemistry: “Aldosterone and Renin.”

UCLA Health: “Renin Test.”

The Merck Manual: “High Blood Pressure (Hypertension.)”

University of Rochester Medical Center:  “Aldosterone and Renin.”

© 2017 WebMD, LLC. All rights reserved.