Plasma renin activity (PRA), also known as the renin (active) assay or random plasma renin, is a measure of the activity of the plasma

enzyme An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...

renin Renin ( etymology and pronunciation), also known as an angiotensinogenase, is an aspartic protease protein and enzyme secreted by the kidneys that participates in the body's renin-angiotensin-aldosterone system (RAAS)—also known as the reni ...

, which plays a major role in the body's regulation of blood pressure, thirst, and urine output. Measure of direct renin concentration (DRC) is technically more demanding, and hence PRA is used instead. DRC assays are still in evolution, and generally a conversion factor of PRA (ng/mL/h) to DRC (mU/L) is 8.2. A recently developed and already commonly used automated DRC assay uses the conversion factor of 12. PRA is sometimes measured, specially in case of certain diseases which present with

hypertension Hypertension, also known as high blood pressure, is a Chronic condition, long-term Disease, medical condition in which the blood pressure in the artery, arteries is persistently elevated. High blood pressure usually does not cause symptoms i ...

hypotension Hypotension, also known as low blood pressure, is a cardiovascular condition characterized by abnormally reduced blood pressure. Blood pressure is the force of blood pushing against the walls of the arteries as the heart pumps out blood and is ...

. PRA is also raised in certain tumors. A PRA measurement may be compared to a plasma

aldosterone Aldosterone is the main mineralocorticoid steroid hormone produced by the zona glomerulosa of the adrenal cortex in the adrenal gland. It is essential for sodium conservation in the kidney, salivary glands, sweat glands, and colon. It plays ...

concentration as an aldosterone-to-renin ratio (ARR).

Measurement and Values

Measurement is done from a sample of venous blood using immunological measuring mechanisms like

ELISA The enzyme-linked immunosorbent assay (ELISA) (, ) is a commonly used analytical biochemistry assay, first described by Eva Engvall and Peter Perlmann in 1971. The assay is a solid-phase type of enzyme immunoassay (EIA) to detect the presence of ...

, RIA, etc. Often these are done by automated machines to minimize human error.

Considerations for variation

Factors to take into account when interpreting results * Age: in patients aged 65 years, renin can be lowered more than aldosterone by age alone, leading to raised ARR. * Gender: premenstrual, ovulating females have higher ARR levels than age-matched men, especially during the luteal phase of the menstrual cycle, during which false positives can occur, but only if renin is measured as Direct renin concentration (DRC) and not as PRA (220). * Time of day, recent diet, posture, and length of time in that posture * State of water intake and hydration * Salt intake * Medications - Use of anti-hypertensive drugs, estrogen-containing forms of

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, anti-anginals drugs, etc. (basically, most drugs that are active on the

heart The heart is a muscular Organ (biology), organ found in humans and other animals. This organ pumps blood through the blood vessels. The heart and blood vessels together make the circulatory system. The pumped blood carries oxygen and nutrie ...

blood vessels Blood vessels are the tubular structures of a circulatory system that transport blood throughout many animals’ bodies. Blood vessels transport blood cells, nutrients, and oxygen to most of the tissues of a body. They also take waste an ...

and/or the

kidneys In humans, the kidneys are two reddish-brown bean-shaped blood-filtering organs that are a multilobar, multipapillary form of mammalian kidneys, usually without signs of external lobulation. They are located on the left and right in the retro ...

) * Level of potassium * Level of creatinine (

kidney failure Kidney failure, also known as renal failure or end-stage renal disease (ESRD), is a medical condition in which the kidneys can no longer adequately filter waste products from the blood, functioning at less than 15% of normal levels. Kidney fa ...

can lead to false-positive ARR) * Certain diseases of the heart, kidneys, etc. * Method of blood collection, including any difficulty doing so

Normal values

Reference ranges for blood tests Reference ranges (reference intervals) for blood tests are sets of values used by a health professional to interpret a set of medical test results from blood samples. Reference ranges for blood tests are studied within the field of clinical chemis ...

of plasma renin activity can be given both in mass and in international units (μIU/mL or equivalently mIU/L, improperly shown as μU/mL or U/L, confusing mcU/mL used where Greek μ not available), with the former being roughly convertible to the latter by multiplying with 11.2.New Assays for Aldosterone, Renin and Parathyroid Hormone
University of Washington, Department of Laboratory Medicine. Retrieved Mars 2011 The following table gives the lower limit (2.5th percentile) and upper limit (97.5th percentile) for plasma renin activity by mass and MCU, with different values owing to various factors of variability of reference ranges:

Results and explanations

''Please go through the physiology of renin and of the

renin–angiotensin system The renin–angiotensin system (RAS), or renin–angiotensin–aldosterone system (RAAS), is a hormone system that regulates blood pressure, fluid, and electrolyte balance, and systemic vascular resistance. When renal blood flow is reduced, ...

to understand why the following occur.'' Higher-than-normal levels may indicate:Different secretory pathways of renin from mouse cells transfected with the human renin gene. 1988 Mar 5; PubMed Free text. Lower-than-normal levels may indicate:

Measurement and Values

Considerations for variation

Normal values

Results and explanations

References

Further reading