The Test Sample
What is being tested?
Aldosterone is a hormone which regulates the retention of sodium (salt) and water by the kidney and also regulates the removal of potassium. It plays an important role in the control of blood pressure.
Aldosterone is produced by the adrenal glands which are located at the top of each kidney. Its production is stimulated by a complex process that includes several other "hormones", the most important of these being renin and angiotensin II. Renin, produced by the kidney, stimulates production of angiotensin II in the bloodstream. Angiotensin II then regulates the release of aldosterone. Normally when renin increases, aldosterone increases; when renin is low, aldosterone decreases.
How is the sample collected for testing?
A blood sample required for measurement of plasma aldosterone and/or renin levels is taken by needle from a vein in the arm. One sample, collected in the morning, usually arround 9am, is usually sufficient for the initial investigation of aldosterone and renin disorders. However, because the levels of aldosterone and renin change when a person moves from lying down to standing up, your doctor may collect one sample whilst you are lying down and another after you have been upright for a few hours.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
You may be asked to adhere to an unrestricted salt diet prior to the test or to temporarily discontinue one or more medications. Please follow any instructions you are given, as this is important to ensure the validity of test results.