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.

Why this test is done

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

How to prepare

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.

Sample type

Blood

Other names for this test

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