Hypertension/High Blood Pressure Health Center

What To Think About

• A renin test is often done at the same time as an aldosterone test. For more information, see the medical test Aldosterone.
• A renin stimulation test may occasionally be done if blood renin levels are low. To prepare for this test, you will eat a low-sodium diet for 3 days. A blood renin level will be drawn and a diuretic, usually furosemide (Lasix), will be put in a vein (intravenous) in your arm. Normally, blood renin levels will increase, but in Conn's syndrome blood renin levels will not change after taking the diuretic.
• Many hospitals now measure renin activity with the renin direct immunoassay, which measures the amount of renin in the blood. A plasma renin activity (PRA) test measures an enzyme called angiotensin I rather than renin itself. A renin direct immunoassay is easier to do and can generally be done instead of the PRA test. However, in some situations (such as pregnancy), PRA results may be more accurate than the renin direct immunoassay.
• If a kidney artery is blocked, another test, such as a captopril test, may be done. For the captopril test, you will take a dose of captopril after the renin assay test is done and your blood pressure is measured. Follow-up blood pressure measurements and a PRA test are done 60 minutes later to find high blood pressure. Other tests that may also be done are duplex Doppler ultrasound or arteriography. For more information, see the medical tests Doppler Ultrasound and Angiogram.