What is being tested?
Aldosterone is a mineral (salt)-retaining steroid, a hormone that directly regulates the retention of sodium (salt) by the kidneys and indirectly regulates the excretion of potassium. It plays an important role in the control of blood volume and blood pressure. Aldosterone is produced by the adrenal cortex, the outer portion of the two adrenal glands that are located at the top of each kidney. It usually takes a chain of events to stimulate the production of aldosterone. The enzyme renin is released by the kidneys when potassium is increased in the blood, sodium is decreased, there is a decrease in the volume of blood in circulation, low blood pressure, and/or when there is decreased blood flow to the kidneys. Renin splits angiotensinogen (a protein created by the liver) to form angiotensin I. Angiotensin-converting enzyme then acts on angiotensin I to form angiotensin II. Angiotensin II constricts blood vessels and stimulates the production of aldosterone. In normal healthy people, when renin increases aldosterone increases; when renin is low, aldosterone decreases.

How is the sample collected for testing?
A blood sample is taken by needle from a vein in the arm to measure plasma aldosterone and/or renin. A 24-hour urine collection for aldosterone is preferred by some physicians since plasma aldosterone levels are variable – they vary throughout the day and are affected by position. Discuss sample collection with your doctor.

Is any test preparation needed to ensure the quality of the sample?
For a plasma aldosterone, your doctor may ask you to be upright or lying down for a couple of hours prior to the blood draw.