Aldosterone and Renin

Aldosterone and renin tests are used to evaluate whether appropriate amounts of aldosterone are being produced and to distinguish between the potential causes of excess or deficiency. Aldosterone may be measured in the blood or in a 24-hour urine sample; renin is always measured in blood. These tests are most useful in screening for primary hyperaldosteronism, also known as Conn syndrome, which causes high blood pressure. If the screening test is positive, aldosterone production may be further evaluated through the use of stimulation and suppression testing.

Both aldosterone and renin levels are highest in the morning and vary throughout the day. They are affected by a person's position, by stress, and by a variety of prescribed medications.

A plasma aldosterone and a plasma renin are usually ordered together when a patient has high blood pressure and a low potassium. Even if potassium is normal, testing may be done if typical medications do not control the high blood pressure or if hypertension develops at an early age. Primary aldosteronism is a potentially curable form of hypertension, so it is important to detect and treat it properly. Aldosterone levels are occasionally ordered, along with other tests, when a doctor suspects that a patient has adrenal insufficiency.

The table below indicates the changes in renin, aldosterone, and cortisol that occur with different disorders.

Primary hyperaldosteronism is caused by the overproduction of aldosterone by the adrenal glands, usually by a benign tumor of one of the glands. The high aldosterone level increases reabsorption of sodium (salt) and loss of potassium by the kidneys, resulting in an electrolyte imbalance. Primary hyperaldosteronism is sometimes called Conn syndrome. Symptoms are not typically present, although muscle weakness can occur if potassium levels are very low. The presence of hypokalemia in a person with hypertension suggests the need to look for hyperaldosteronism.

Secondary hyperaldosteronism, which is more common, can occur as a result of anything that decreases blood flow to the kidneys, decreases blood pressure, or lowers sodium levels. The most important cause is narrowing of the blood vessels that supply the kidney, termed renal artery stenosis. This causes high blood pressure due to high renin and aldosterone that may be cured by surgery or angioplasty. Sometimes, to see if only one kidney is affected, a catheter is inserted through the groin and blood is collected directly from the veins draining the kidney (renal vein renin levels); if the value is significantly higher in one side, this indicates where the narrowing of the artery is present. Similarly, blood may sometimes be taken from both of the adrenal veins to determine whether there is a difference in the amount of aldosterone (and sometimes cortisol) produced by each of the adrenal glands. Secondary hyperaldosteronism may also be seen with congestive heart failure, cirrhosis, kidney disease, and toxemia of pregnancy.

A low aldosterone (hypoaldosteronism) usually occurs as part of adrenal insufficiency; it causes dehydration, low blood pressure, and low blood levels of sodium and potassium. In infants with congenital adrenal hyperplasia, the infant lacks an enzyme needed to make cortisol; in some cases, this also decreases production of aldosterone. This is a rare cause of low aldosterone.

The amount of salt in the diet and medications, such as over-the-counter pain relievers of the non-steroid class, diuretics, beta blockers, steroids, angiotensin-converting enzyme (ACE) inhibitors, and oral contraceptives can affect the test results. Some of these drugs are used to treat high blood pressure. Your doctor will tell you if you should change the amount of sodium (salt) you ingest in your diet, your use of diuretics or other medications, or your exercise routine before aldosterone testing.

Aldosterone levels become very low with severe illness, so testing should not be done at times when a person is very ill. Stress and strenuous exercise can temporarily increase aldosterone values.