Aldosterone and Renin

The ratio between these two hormones compared with the aldosterone level can be a very helpful investigation. These results together with cortisol, can give important information about some of the hormone disorders associated with the adrenals and kidneys indicated in the table below

Primary hyperaldosteronism (Conn's syndrome) is caused by the overproduction of aldosterone in the adrenal glands, usually by a benign tumour of one of the glands. The high aldosterone level increases reabsorption of sodium (salt) and water and the loss of potassium by the kidneys, resulting in high blood pressure (also called 'hypertension'). Also muscle weakness can occur if potasium levels are very low.

Secondary hyperaldosteronism is more common and can occur as a result of anything that decreases blood flow to the kidneys, decreases blood pressure, or lowers salt levels. The most important cause is narrowing of the blood vessels that supply the kidney, called 'renal artery stenosis'. This stimulates production of renin and aldosterone, which in turn leads to raised blood pressure. 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. Renin is then measured in these blood samples. If the value is significantly higher in one side, this indicates the site of the narrow artery. Other causes of secondary hyperaldosteronism include congestive heart failure, cirrhosis of the liver, kidney disease, and pre-eclampsia in pregnancy.

Hypoaldosteronism (i.e. a lack of aldosterone) usually occurs as part of adrenal insufficiency (Addison's disease). It causes dehydration, low blood pressure, high potassium (hyperkalaemia) and low sodium (hyponatraemia) in the blood.

Aldosterone and renin tests are usually requested together. High blood pressure together with a low potassium usually leads the doctor to check these two tests. Aldosterone levels are sometimes used in persons suspected of having poor adrenal function. Some doctors use aldosterone and renin levels to point to the likely treatments that will be effective in persons with high blood pressure.

The changes in plasma aldosterone, cortisol, and renin are summarized in the table earlier. High levels of serum and urine aldosterone, along with a low plasma renin, indicate primary hyperaldosteronism (Conns syndrome). Secondary hyperaldosteronism, on the other hand, is indicated by an increase in both aldosterone and renin.

A low aldosterone is usually part of adrenal insufficiency (Addison's disease). In infants with a condition called congenital adrenal hyperplasia, the infant lacks an enzyme needed to make cortisol; in some cases, this also decreases production of aldosterone which is a rare cause of low aldosterone.

The amount of salt in the diet and medicines, such as over-the-counter pain relievers of the non-steroid class (such as Nurofen and Hedexl), diuretics (water pills), beta blockers, steroids, angiotensin-converting enzyme (ACE) inhibitors, and oral contraceptives can affect the test results. Many 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 and renin are tested.

Aldosterone levels can fall to very low levels with severe illness, so testing should be done after recovery.