What is a renin test?

This test measures the level of renin in your blood. Renin is an enzyme, a protein that speeds up certain chemical reactions in your body. It's made by your kidneys. When your blood pressure or sodium decreases or your potassium increases, your kidneys release renin. That's because renin also acts as a hormone (a chemical messenger in your bloodstream that controls the actions of certain cells or organs) to help control your blood pressure.

Renin controls the production of another hormone called aldosterone, which is made in your adrenal glands. These are two small glands located above the kidneys. Aldosterone helps keep your blood pressure stable. It does this by helping to balance the levels of two electrolytes in your blood: potassium and sodium.

Usually, if renin increases or decreases, aldosterone does the same. These levels are highest in the morning and change throughout your day. Your position (sitting, standing, etc.), stress level, and certain medicines can affect your renin and aldosterone levels.

If your renin and/or aldosterone levels are not normal, it can be a sign of an adrenal gland disorder. Because the two hormones work together, an aldosterone test is often done at the same time as a renin test.

Other names: renin blood test, plasma renin activity (PRA) aldosterone-renin ratio (ARR)

What is it used for?

A renin test (or renin and aldosterone test) is used to find out if your adrenal glands are making too much or too little aldosterone.

The test is especially useful in diagnosing primary aldosteronism (PA), a disease caused by having too much aldosterone. PA, also known as primary hyperaldosteronism or Conn syndrome, causes high blood pressure. If not treated, high blood pressure may increase your risk of stroke, heart attack, and kidney failure.

Why do I need a renin test?

You may need a renin test if you've been diagnosed with high blood pressure, especially if it doesn't respond well to standard blood pressure medicines. The test can show whether PA is causing the condition.

Sometimes, PA causes low potassium levels, so you may also need this test if you have symptoms of low potassium. Your symptoms can vary, depending on the cause and how low your potassium level is. The symptoms can include:

• Muscle cramps
• Muscle weakness
• Excessive thirst
• Fatigue
• Headache
• Constipation
• Racing heartbeat

What happens during a renin test?

A health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.

Will I need to do anything to prepare for this test?

You may be asked to stop taking certain medicines before your test, so tell your health care provider about everything you take. But don't stop taking any medicines unless your provider tells you to. Some medicines that may affect the results of your test can include:

• Birth control pills
• Blood pressure medicines
• Diuretics (water pills)

You may also be asked to limit the amount of salt you eat each day before your test. Your provider will explain how to do this and for how long.

Are there any risks to this test?

There is very little risk to having a blood test. There may be slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.

What do the results mean?

If your results show a higher-than-normal amount of renin, it may be a sign of:

• Addison disease (also called adrenal insufficiency), a condition in which your adrenal glands don't make enough of certain hormones
• Cirrhosis, scarring of the liver
• Dehydration

If your results show a lower-than-normal amount of renin, it may be a sign of:

• Primary aldosteronism (PA)
• Kidney disease

Most often, your renin test results will be compared with your aldosterone test results. These results may show one of the following:

• Lower than normal renin/Lower than normal aldosterone. This may mean you have Cushing's syndrome, a disorder in which the adrenal glands make too much of a hormone called cortisol.
• Lower than normal renin/Higher than normal aldosterone. This may mean you have PA.
• Higher than normal renin/Lower than normal aldosterone. This may mean you have Addison disease.
• Higher than normal renin/Higher than normal aldosterone. This may mean you have secondary aldosteronism. With this disorder, your adrenal glands are healthy, but another medical condition is causing them to make too much aldosterone. These conditions can include diseases of the heart, liver, and kidneys.

Depending on your results, your provider may recommend medicines and/or diet and lifestyle changes to treat your condition.

If you have questions about your results, talk to your provider.

Learn more about laboratory tests, reference ranges, and understanding results.

Is there anything else I need to know about a renin test?

You should not eat natural black licorice for at least two weeks before your test, because it can affect your results. Most licorice products in the United States don't contain natural licorice. Before you eat any licorice, check the ingredients label to be sure.