Plasma renin activity | |
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Purpose | measure of the activity of the plasma enzyme renin, |
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 renin, 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. [1] PRA is sometimes measured, specially in case of certain diseases which present with hypertension or hypotension. PRA is also raised in certain tumors. [2] A PRA measurement may be compared to a plasma aldosterone concentration as an aldosterone-to-renin ratio (ARR).
Measurement is done from a sample of venous blood using immunological measuring mechanisms like ELISA, RIA, etc. Often these are done by automated machines to minimize human error.
Factors to take into account when interpreting results [1]
Reference ranges for blood tests 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. [3] 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:
Unit | Lower limit | Upper limit |
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ng/(mL*hour) | 0.29, [4] 1.9 [5] | 3.7 [4] [5] |
μIU/mL | 3.3, [3] 21 [6] | 41 [3] [6] |
Please go through the physiology of renin and of the renin–angiotensin system to understand why the following occur.
Higher-than-normal levels may indicate: [7] [8] [9] [10] [11]
Disease | Brief Description |
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Addison's disease | Kidneys trying to counter low aldosterone output. |
Cirrhosis of the liver | RAAS activates as a compensatory response to the splanchnic arterial vasodilation due to portal hypertension |
Essential hypertension | Just more of renin is being secreted by the kidneys. |
Hemorrhage (bleeding) | Kidneys trying to raise falling blood pressure. |
Hypokalemia | Kidneys trying to raise falling blood pressure due to reduced cardiac output. |
Malignant hypertension | Excessive renin is being secreted by the kidneys. |
Renin-producing renal tumors | Tumors can secrete substances like this. See tumor markers |
Renovascular hypertension | Renal vascular damage leading to reduced JGA perfusion. |
Lower-than-normal levels may indicate:
Disease | Brief Description |
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ADH therapy | Leads to water retention and thus raised blood pressure. |
Salt-retaining steroid therapy | see above |
Salt-sensitive essential hypertension | see above |
Primary Hyperaldosteronism | see above and direct inhibition of aldosterone on renin secretion |
Angiotensin-converting-enzyme inhibitors are a class of medication used primarily for the treatment of high blood pressure and heart failure. They work by causing relaxation of blood vessels as well as a decrease in blood volume, which leads to lower blood pressure and decreased oxygen demand from the heart.
The endocrine system is a messenger system comprising feedback loops of the hormones released by internal glands of an organism directly into the circulatory system, regulating distant target organs. In vertebrates, the hypothalamus is the neural control center for all endocrine systems. In humans, the major endocrine glands are the thyroid gland and the adrenal glands. The study of the endocrine system and its disorders is known as endocrinology.
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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.
Angiotensin is a peptide hormone that causes vasoconstriction and an increase in blood pressure. It is part of the renin–angiotensin system, which regulates blood pressure. Angiotensin also stimulates the release of aldosterone from the adrenal cortex to promote sodium retention by the kidneys.
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Parathyroid hormone (PTH), also called parathormone or parathyrin, is a peptide hormone secreted by the parathyroid glands that regulates the serum calcium concentration through its effects on bone, kidney, and intestine.
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Renal physiology is the study of the physiology of the kidney. This encompasses all functions of the kidney, including maintenance of acid-base balance; regulation of fluid balance; regulation of sodium, potassium, and other electrolytes; clearance of toxins; absorption of glucose, amino acids, and other small molecules; regulation of blood pressure; production of various hormones, such as erythropoietin; and activation of vitamin D.
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Aldosterone synthase, also called steroid 18-hydroxylase, corticosterone 18-monooxygenase or P450C18, is a steroid hydroxylase cytochrome P450 enzyme involved in the biosynthesis of the mineralocorticoid aldosterone and other steroids. The enzyme catalyzes sequential hydroxylations of the steroid angular methyl group at C18 after initial 11β-hydroxylation. It is encoded by the CYP11B2 gene in humans.
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