ALDOSTERONE / PLASMA RENIN ACTIVITY RATIO

Aldosterone/Plasma Renin Activity Ratio, commonly called the Aldosterone-Renin Ratio (ARR), is a blood test used primarily to screen for primary aldosteronism. It measures aldosterone concentration and plasma renin activity and then calculates the relationship between the two results.

Aldosterone and renin work together to control blood pressure, sodium, potassium, and fluid balance. In primary aldosteronism, aldosterone production may remain inappropriately high while renin activity is suppressed. This pattern can produce an elevated ARR.

Benefits of the Test

• Measures aldosterone and plasma renin activity from blood samples.
• Calculates the aldosterone-to-renin ratio.
• Supports screening for primary aldosteronism.
• Helps investigate resistant or difficult-to-control hypertension.
• Supports evaluation of hypertension with low potassium.
• May identify a potentially treatable cause of high blood pressure.
• Helps assess the renin-angiotensin-aldosterone system.
• Can guide the need for confirmatory endocrine testing.
• Supports evaluation of selected adrenal-gland abnormalities.
• Provides laboratory information for specialist treatment planning.

Why Doctors Recommend This Test

Doctors may recommend ARR screening when a patient has persistent hypertension despite multiple medicines, severe hypertension, hypertension developing at a young age, unexplained low potassium, an adrenal mass, sleep apnoea with hypertension, or a family history of early-onset hypertension or stroke.

The test may also be advised when primary aldosteronism has been diagnosed in a close relative. ARR is a screening test and an abnormal result generally requires specialist interpretation and confirmatory evaluation.

Preparation Before Test

• The sample is often collected in the morning under standardised conditions.
• Follow instructions about sitting, standing, walking, or resting before collection.
• Maintain usual salt intake unless your doctor prescribes a specific plan.
• Low potassium should be corrected under medical supervision before testing when possible.
• Inform the doctor about all blood-pressure medicines, diuretics, steroids, and supplements.
• Do not stop or change medicines without medical supervision.
• Inform the doctor about potassium supplements and liquorice-containing products.
• Avoid strenuous exercise immediately before sample collection.
• Tell the doctor about pregnancy, kidney disease, heart failure, or recent severe illness.
• Follow the laboratory’s timing, posture, and sample-handling instructions precisely.

Normal Reporting Time

The Aldosterone/Plasma Renin Activity Ratio requires specialised hormone analysis and calculation after both results are validated. Reports are generally available within a few working days after sample collection, processing, analysis, and quality review. Exact reporting time may vary according to the testing schedule and laboratory workflow.

Who Should Take This Test?

This test may be recommended for:

• Patients with resistant hypertension.
• Individuals with severe or persistently uncontrolled blood pressure.
• Patients with hypertension and unexplained low potassium.
• Individuals who developed hypertension at a young age.
• Patients with hypertension and an adrenal incidentaloma.
• Individuals with hypertension and obstructive sleep apnoea.
• Patients with a family history of early hypertension or stroke.
• First-degree relatives of patients diagnosed with primary aldosteronism.
• Individuals requiring assessment of adrenal and renin function.
• People specifically advised to undergo ARR testing by an endocrinologist.

Detailed Information

Renin is an enzyme released by specialised cells in the kidneys when blood pressure, blood volume, or sodium delivery to the kidneys decreases. Renin begins a hormonal pathway that produces angiotensin II, which constricts blood vessels and stimulates aldosterone release.

Aldosterone is produced by the zona glomerulosa of the adrenal cortex. It signals the kidneys to retain sodium and water while increasing potassium excretion. These effects help maintain circulating volume and blood pressure.

Under normal conditions, renin and aldosterone respond together. When renin activity increases, aldosterone usually rises. When sodium and blood volume are adequate, renin activity generally decreases and aldosterone production is reduced.

In primary aldosteronism, one or both adrenal glands produce aldosterone inappropriately. The resulting sodium retention and increased blood volume suppress renin. Therefore, the typical screening pattern is an inappropriately elevated aldosterone level combined with low plasma renin activity.

Primary aldosteronism may be caused by an aldosterone-producing adrenal adenoma, bilateral adrenal hyperplasia, or less commonly inherited or other adrenal disorders. It is an important potentially treatable cause of secondary hypertension.

The ARR is calculated by dividing the aldosterone concentration by plasma renin activity. The numerical ratio depends on the units and analytical methods used. A cut-off obtained from another laboratory should not be applied directly to an individual report.

A high ratio does not independently confirm primary aldosteronism. A very low renin result can produce a high ratio even when aldosterone is not clearly elevated. Doctors assess the individual aldosterone and renin results as well as the calculated ratio.

Many factors influence the test. Sodium intake, potassium concentration, posture, collection time, age, kidney function, menstrual status, pregnancy, stress, and medicines may change aldosterone, renin, or both.

Mineralocorticoid-receptor antagonists, diuretics, beta-blockers, ACE inhibitors, angiotensin-receptor blockers, direct renin inhibitors, and some calcium-channel blockers may affect interpretation. Medicine changes must only be made by the treating doctor because uncontrolled hypertension can be dangerous.

Low potassium can reduce aldosterone secretion and potentially produce a misleading result. Potassium abnormalities are therefore often corrected before testing under medical supervision.

Posture affects renin and aldosterone. Results obtained after lying down may differ from results collected after standing, walking, or sitting. The doctor and laboratory should specify the required posture and rest period.

If screening is positive, the doctor may recommend a saline-infusion test, oral sodium-loading test, captopril-challenge test, or another suppression procedure. Subsequent evaluation may include adrenal CT and adrenal-vein sampling to determine whether excess hormone production comes from one adrenal gland or both.

At Focus Diagnostics, aldosterone and plasma renin activity testing is performed using established biochemical methods, controlled sample-handling procedures, and laboratory quality standards to provide reliable results for endocrine interpretation.