The renin-aldosterone ratio is a value that is calculated after measuring the concentrations of the hormones renin and aldosterone in the blood. It is most commonly checked as part of a diagnostic evaluation of high blood pressure, also known as hypertension. Both of these hormones are part of the renin-angiotensin system (RAS) that helps the body maintain blood pressure. Checking the renin-aldosterone ratio can provide information about whether renin or aldosterone levels are high relative to one another. A high ratio most often points to a narrowing of the arteries feeding the kidneys, whereas a low ratio suggests that an aldosterone-producing tumor is present.
In order to understand why the renin-aldosterone ratio yields important information about possible pathologic processes occurring in a patient, it helps to understand what these hormones do and how they are related. Renin is a hormone that is made by the kidney, and is secreted in response to stimuli such as low blood pressure or low blood flow through the renal system. As part of the RAS, renin activates another hormone called angiotensin, which serves a number of purposes. It can increase blood pressure through arterial vasoconstriction, or the narrowing of the vessels that carry blood from the heart to distant regions of the body. Angiotensin also helps release aldosterone, another hormone that can increase blood pressure, from the adrenal glands.
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As renin and aldosterone are part of an interrelated system called the RAS that serves the important physiologic purpose of maintaining sufficient blood pressure, any time one element of this system is overactive, the affected patient can develop hypertension, or high blood pressure. Based solely on knowing that a patient has an elevated blood pressure, it is difficult to tell whether one of these hormones is the root cause of this problem. For this reason, in select patients who have hard-to-control blood pressure that is resistant to antihypertensive medications, the renin-aldosterone ratio is checked.
A high renin-aldosterone ratio suggests that too much renin is being produced by the body. Rarely, this can be due to a specialized tumor that is producing this hormone. More frequently, however, the renin level is elevated because there is a narrowing of the artery supplying blood to the kidney, a condition that most commonly happens as a result of atherosclerosis. The renin is overproduced because only a low blood flow reaches the kidneys due to the narrowing of the arteries.
Having a low renin-aldosterone ratio suggests a problem with overproduction of aldosterone. Normally, the RAS is needed for aldosterone to be released from the adrenal glands. If there is a tumor in the adrenal gland that produces aldosterone, a condition called Conn syndrome results, which causes hypertension and problems with the electrolyte content of the blood. Aldosterone-producing tumors can often be removed through surgery, allowing the patient's high blood pressure to return to the normal range.