Aldosterone is a corticosteroid hormone that is secreted by the cortex of the adrenal gland. It increases the re-absorption of sodium and water and it also releases potassium in the kidneys. All of this causes an increase in blood volume and therefore an increase in blood pressure. Therefore, an aldosterone test is used to study whether the correct amount of aldosterone is being produced by the adrenal gland and also to find out the reason behind any excess or deficiency. Aldosterone levels can be measured using either a blood test or a 24-hour urine sample. Both these tests can screen a person for primary hyperaldosteronism, commonly known as Conn’s syndrome, which is responsible for causing high blood pressure. In case of positive test results, aldosterone levels can be further assessed through stimulation and suppression testing. Aldosterone levels tend to peak in the early morning and then vary as the day progresses. These levels are mostly affected by stress; however, certain medications can also cause aldosterone levels to fluctuate.
A doctor may ask a patient to undergo an aldosterone plasma test if the person suffers from high blood pressure but has low levels of potassium in his or her blood. This test is also ordered if medications to reduce or control high blood pressure fail to work or if a person develops hypertension at a very young age. Primary aldosteronism is a curable form of hypertension and it is therefore important to detect this disorder and treat it promptly. An aldosterone plasma test could also be ordered if the doctor suspects adrenalin insufficiency.
For the blood test, a small amount of blood is extracted from a vein in the forearm. The blood is tested for aldosterone plasma or rennin. A blood sample could also be taken from the renal or adrenal veins, but this is done using a catheter and requires to be done by a trained radiologist in a hospital. Another test is the 24-hour urine test for aldosterone. Some doctors prefer the urine test because plasma aldosterone levels tend to fluctuate during the day and this can be noted in the urine sample.
Aldosterone levels are affected by your position and so before the aldosterone plasma blood test the doctor may recommend an upright or lying down posture for a particular amount of time, usually not more than 30 minutes.