What is Aldosterone?
Aldosterone is a hormone produced in the adrenal glands. It is a key component along the renin-angiotensin-aldosterone-system (RAAS) axis, an endocrine system that helps regulate blood pressure, electrolytes and fluids. When activated, aldosterone causes the body to hold onto more salt and water, causing blood pressure to go up.
However, despite its key role in regulating blood pressure, aldosterone can sometimes be overproduced in the body independent of signals from the RAAS. Detecting high amounts of aldosterone is the first step toward diagnosing primary aldosteronism. High aldosterone levels can also lead to low plasma potassium levels.
A rise in blood aldosterone levels causes secondary hypertension, which is usually difficult to treat. Secondary hypertension caused by primary aldosteronism differs from essential hypertension (also called primary hypertension). Essential hypertension isn’t caused by a medical condition. Aldosterone overproduction is sometimes the result of an adenoma causing hyperactivity and high aldosterone.
An estimated 1.5% to 5% of hypertensive patients globally with primary aldosteronism have an adenoma. Possible causes of primary aldosteronism and increased aldosterone in the blood include bilateral adrenal hyperplasia or even malignant cancerous tumors.
Because another medical condition causes secondary hypertension, it can be more challenging to treat. In fact, patients often take multiple hypertension medications to keep aldosterone in check. Hypertension that is difficult to treat can lead to a range of complications, including heart disease and chronic kidney disease (CKD).
What is Renin?
Renin is an enzyme produced by the kidneys that plays an important role in managing blood pressure. In fact, renin kickstarts the body’s RAAS system.
When blood pressure gets too low, and the RAAS is activated, the kidney secretes renin into the bloodstream. The presence of renin causes a cascade of signaling reactions: renin converts to angiotensin I, which triggers the production of angiotensin II, which facilitates the production of aldosterone. The presence of aldosterone forces the body to hold on to more salt and water. As a result, blood pressure goes up. In other words, the secretion of renin causes blood pressure to rise.
What is the Aldosterone to Renin Ratio?
The aldosterone to renin ratio refers to the amount of aldosterone in the blood compared to the amount of renin. Normally, this ratio is relatively balanced because the RAAS maintains an equilibrium between the two. That’s because, in the RAAS, more renin activity leads to increased aldosterone production. Once the body produces aldosterone, helping restore normal blood pressure, renin activity reduces, signaling that less aldosterone is needed.
However, in people with primary aldosteronism, aldosterone is overproduced independent of signals from the RAAS. As a result, aldosterone remains high even if renin has become less active, changing the ratio of aldosterone to renin.
What Factors Affect the Aldosterone to Renin Ratio?
Several factors can affect the aldosterone to renin ratio. These include changes in dietary salt intake, pregnancy and stress. Taking certain medications for hypertension can also affect the balance between aldosterone and renin. Common medications for treating primary aldosteronism (such as mineralocorticoid receptor antagonists (MRAs) that target aldosterone production) can cause low aldosterone levels.
How is the Aldosterone to Renin Ratio Tested?
A simple blood test called the aldosterone renin ratio test (also called an ARR or renin test) is used to test the aldosterone to renin ratio. This common screening test detects primary aldosteronism. Other tests, such as aldosterone suppression tests, use high salt diets or saline infusions to measure how aldosterone changes. Switching a patient to an aldosterone-targeting medication could also reveal aldosterone abnormalities.
What is Measured in the Aldosterone Renin Ratio Test?
The aldosterone renin ratio test measures plasma aldosterone concentrations and how active renin enzymes are, or plasma renin activity (PRA). Other tests, such as direct renin concentration tests, can also measure plasma renin activity.
What do Results Mean?
Generally, a high level of aldosterone compared to renin is usually the first step toward detecting and diagnosing primary aldosteronism. In a normally functioning RAAS, renin and aldosterone are sensitive to each other. As a result, they normally increase and decrease consistently compared to one another. For example, when blood pressure stabilizes following increased renin activity and aldosterone production, the kidneys produce less renin. When renin becomes less active, so does aldosterone production. If aldosterone is high while renin is low, it could signal that something isn’t working correctly in the system.
A salt-diet test determines if aldosterone drops in the presence of high levels of salt. Aldosterone is needed only when the body needs to hold on to more salt. If aldosterone remains high after following a high-salt diet, it could indicate primary aldosteronism.
As a screening test, the results of an aldosterone renin ratio test are only preliminary. Confirmatory testing is usually needed to diagnose a condition like primary aldosteronism correctly.
How Accurate is the Aldosterone Renin Ratio Test?
The test is a fairly accurate way of detecting and screening for primary aldosteronism. However, these tests are a “sensitive” type of test, which means they are more likely to trigger a false-positive result.
As a result, the aldosterone renin ratio test is just the first step in diagnosing primary aldosteronism. If the ratio test detects high levels of aldosterone, then another test is needed to confirm these high aldosterone levels and locate why the body is producing aldosterone independent of signals from the RAAS. For example, these tests could include scans to identify an aldosterone-producing adenoma. An adrenal venous sampling may also confirm that the adrenal glands are causing an overproduction of aldosterone. Medications that silence aldosterone regulators in the RAAS can also rule out aldosterone production abnormalities.
How can you Prepare for the Test?
Because these tests are very sensitive, many things can affect results, including what you are doing before and leading up to giving a blood sample for the test. Some of these factors include the following:
- When the sample is taken
- How active you are during the day
- Any medications you might be taking
Aldosterone is usually highest in the morning after someone has been able to move around. As a result, patients are typically asked to give a blood sample a few hours after waking up and having time to get their bodies moving.
Hypertensive patients may need to change their medications before giving blood for the test. Medications such as angiotensin converting enzyme inhibitors (ACE) impact hormone levels (including the amount of aldosterone). MRA medications also suppress aldosterone production. Having these medications in the bloodstream can compromise the accuracy of results, causing the test to deliver a false-positive result.
It used to be considered ideal for a patient to stop taking all hypertension medications before giving blood for the test. However, this is no longer considered safe. Instead, patients are often asked to switch to medications known to have a minimal effect on hormone levels before giving blood for the aldosterone renin ratio test.