Plasma renin activity test
Quick answer: This test measures the activity of renin, a kidney hormone that helps control blood pressure and salt balance. It is often ordered with aldosterone to look for hormone causes of high blood pressure, especially when blood pressure is hard to control or potassium is low.
- SampleBlood
- TakesAbout 5 minutes, sometimes with 15 to 30 minutes of sitting or standing first
- Before the testPosture, time of day, salt intake and some blood pressure medicines affect the result, so follow your doctor's instructions and do not stop any medicine on your own.
How the test is done
- 1You follow any instructions about posture, salt and medicines given by your doctor
- 2You may be asked to sit or stand for a set time before the sample
- 3Blood is drawn, often with an aldosterone test at the same time
- 4The sample is processed promptly in the lab
What your results can mean
Reading your report
Normal ranges differ between labs, so compare your result with the range printed on your report and discuss it with your doctor.
If the result is outside the usual range
A low renin with a high aldosterone can point to primary aldosteronism, a hormone cause of high blood pressure. A high renin can be seen with narrowed kidney arteries, dehydration, low salt intake or some blood pressure medicines.
Who usually has this test
People with high blood pressure that is hard to control, high blood pressure at a young age, or high blood pressure with low potassium.
Risks and aftercare
You can resume your usual position and routine after the sample, and a small bruise is possible.
Names and options
Also called: PRA, renin test, renin activity
Listed by the hospital as
- RENIN ACTIVITY, PLASMA
Questions about this test
What is the aldosterone renin ratio?
It compares aldosterone with renin in the same sample and is a common first test for primary aldosteronism. A high ratio usually leads to further confirmatory tests.
Do blood pressure medicines affect renin?
Yes. Many blood pressure medicines raise or lower renin. Your doctor may plan changes before the test, but you should not stop or change any medicine on your own.
Why does posture matter for this test?
Renin changes when you move from lying to standing. Labs set a standard posture and time so results can be compared with their reference values.
Related tests
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This page explains each test in general terms so you know what to expect. It is not medical advice: your doctor decides which tests you need and what your results mean. Reference ranges differ between laboratories. Updated 4 November 2026.