Plasma Renin Activity (PRA)
Measures how active renin is in your blood. Renin is a kidney enzyme that helps control blood pressure and salt balance.
AI-verified against cited sources. Awaiting expert reviewAlso called PRALOINC 2915-7
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What it is
Renin is an enzyme your kidneys release when blood pressure or salt levels drop. It starts a chain of steps that tightens blood vessels and tells the adrenal glands to make aldosterone, a hormone that makes the body hold on to salt and water. This test measures how fast the renin in your blood sample makes a substance called angiotensin I, reported as ng/mL per hour. It is not the same as the "direct renin" test, which counts renin molecules instead.
Why it matters
Doctors often order renin together with aldosterone when they are looking into hormone-related causes of high blood pressure or low potassium. Low renin with high aldosterone is a pattern clinicians check for primary aldosteronism, an adrenal cause of high blood pressure. High renin often means the body is responding to low blood flow or salt loss. Posture, salt intake, age and many medicines change renin, so the way the sample is collected matters.
If it’s low
Lower-than-usual renin means the system is less active. This is common with a high-salt diet, older age and reduced kidney function, and with beta-blockers, clonidine, methyldopa and NSAID pain relievers. Low renin together with a high aldosterone is a pattern doctors check when they are looking into primary aldosteronism, an adrenal cause of high blood pressure. Your clinician can interpret it together with aldosterone and potassium.
Common causes
- A high-salt diet
- Older age
- Reduced kidney function
- Beta-blockers, clonidine, methyldopa and NSAIDs
- Eating large amounts of real licorice
- Primary aldosteronism, an adrenal condition in which too much aldosterone is made
What can help
- Ask which of your medicines could lower renin and whether that matters for this test
- Ask whether aldosterone and potassium were checked at the same time
If it’s high
Higher-than-usual renin means the system that raises blood pressure and holds on to salt is more active than usual. Common reasons are everyday ones, such as cutting back on salt, taking a diuretic, an ACE inhibitor or an ARB, or standing or walking before the draw. Less often, high renin goes with reduced blood flow to a kidney, heart failure with fluid build-up, a salt-wasting condition such as Bartter syndrome, or too little steroid replacement in adrenal insufficiency. Your clinician can interpret it together with aldosterone and potassium.
Common causes
- A low-salt diet, or salt and fluid loss
- Diuretics (including spironolactone), ACE inhibitors, ARBs and dihydropyridine calcium channel blockers
- Standing or walking before the draw
- Pregnancy
- Narrowing of the artery that supplies a kidney (renovascular hypertension)
- Heart failure with fluid build-up
- Bartter syndrome and other rare salt-wasting conditions
- Too little steroid replacement in adrenal insufficiency
- Rarely, a tumor that makes renin
What can help
- Ask your clinician how your salt intake, posture and medicines may have affected the result
- Ask whether the test should be repeated under standard conditions, such as a morning draw while seated
- Don't change your salt intake or any medicine on your own before a repeat test
Usual ranges
What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.
The usual range depends on age. Choose an age to see the one that applies.
- 16+0.17–5.38 ng/mL/h
Sources: Labcorp, Quest Diagnostics, ARUP Laboratories, Mayo Clinic Laboratories
See Renin activity by age and sex, with the U.S. survey numbers where they exist.
What can affect your result
- Posture: standing or walking raises renin, and lying down lowers it
- Time of day: levels are highest early in the morning and fall during the day
- Salt intake: low salt raises renin and high salt lowers it
- Medicines, including diuretics, ACE inhibitors, ARBs, beta-blockers and NSAIDs
- Age and kidney function: renin falls with age and with reduced kidney function
- Pregnancy raises renin
- Cold handling: chilled tubes or ice can raise the result falsely, so labs ask for room-temperature handling
- Posture: standing or walking before the draw raises renin, and lying down lowers it.
- Salt intake: a low-salt diet raises renin and a high-salt diet lowers it.
- Medicines that tend to raise renin include diuretics (including spironolactone), ACE inhibitors, ARBs and dihydropyridine calcium channel blockers.
- Medicines that tend to lower renin include beta-blockers, clonidine, methyldopa and NSAIDs.
- Cold: chilled tubes or ice can activate prorenin and falsely raise the result. Labs ask for room-temperature handling and prompt freezing of the plasma.
- Time of day: renin is highest early in the morning and falls during the day.
Morning to mid-morning, seated or after being up and about for 30 minutes to 2 hours, depending on the lab Reflects your state at the time of the draw, including posture, salt intake and medicines.
When to talk to a clinician
Renin results are rarely urgent on their own. Talk with your clinician about a result outside your lab's range, especially together with a high aldosterone, a low potassium or high blood pressure readings. If you feel unwell, for example with chest pain, trouble breathing, confusion or fainting, call 911 or your local emergency number.
Questions you could ask
- Why was this test ordered for me?
- Which of my medicines could change renin or aldosterone results?
- Could my salt intake, posture or any of my medicines explain this result?
- Was my blood drawn the way the lab asked, and should we repeat it under standard conditions?
- Should aldosterone and potassium be looked at along with it?
- Could any of my medicines or my salt intake explain a low result?
Questions people ask
Why does my renin result depend on whether I was lying down or standing?
Standing up lowers blood flow to your kidneys a little, so they release more renin. That is why labs ask about your posture and why some print separate ranges for lying down and upright. Labcorp asks you to walk around for about 30 minutes before the draw, while others ask you to sit for 5 to 15 minutes after being up for a couple of hours.
What is the difference between renin activity and direct renin?
Renin activity measures how fast the renin in your sample makes angiotensin I. Direct renin counts the active renin molecules. The results use different units and ranges and are not interchangeable, so compare each only with the range printed for that test.
How do I convert ng/mL/h to ng/L/s?
Multiply ng/mL/h by 0.278 to get ng/L/s. Going the other way, multiply ng/L/s by 3.6. Micrograms per liter per hour (µg/L/h) is the same number as ng/mL/h.
Show the science and sources
Units
- 1 ng/mL/h = 1 ng/mL/h
- 1 ng/mL/h = 0.2778 ng/L/s
- 1 ng/mL/h = 0.01667 ng/mL/min
Open the Renin activity unit converter
For clinicians and researchers
PRA measures the rate at which plasma renin generates angiotensin I from the sample's own angiotensinogen, reported in ng/mL/h. Labcorp and Quest quantify angiotensin I by LC-MS/MS; ARUP lists an ELISA. Because the reaction depends on angiotensinogen supply, PRA can read normal when angiotensinogen is raised (luteal phase, exogenous estrogen) even though renin concentration is low, whereas direct renin assays are not affected (Labcorp). Cold activates prorenin and falsely raises results, so tubes are kept at room temperature, spun in a non-refrigerated centrifuge and the plasma frozen quickly (Labcorp, ARUP). Mayo describes a serum aldosterone (ng/dL) to PRA (ng/mL/h) ratio of 20 or more, with aldosterone of at least 15 ng/dL, as probable primary aldosteronism. Published aldosterone-to-renin cut-offs depend on the assay and units; the 2023 Korean guideline lists 20, 30 and 40 for aldosterone in ng/dL over PRA in ng/mL/h and describes a PRA under 1 ng/mL/h as the very low renin seen in primary aldosteronism, with a practical detection limit of 0.2 ng/mL/h. ACE inhibitors can falsely raise PRA (Mayo), and a mineralocorticoid receptor antagonist raises renin, so a still-suppressed renin on one supports primary aldosteronism (Korean guideline). PRA and direct renin concentration are not interchangeable; the commonly quoted PRA-to-DRC conversion (8.2 mU/L per ng/mL/h, or 12 for DiaSorin assays) is only approximate. Intervals vary widely with posture, sodium status and age: adult upper limits for a normal-sodium diet run from 1.6 (ARUP, lying down) to 5.82 ng/mL/h (Quest).
LOINC 2915-7 (primary), 17516-6, 2918-1. Specimen: plasma.
Sources
- Renin Activity, Plasma (test 002006), Labcorp
- Plasma Renin Activity, LC/MS/MS (test 16846), Quest Diagnostics
- Renin Activity (test 0070105), ARUP Laboratories
- Renin Activity, Plasma (test PRA), Mayo Clinic Laboratories
- 2023 Korean Endocrine Society Consensus Guidelines for the Diagnosis and Management of Primary Aldosteronism, Endocrinology and Metabolism (Seoul) (2023)
AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.