Aldosterone and Renin

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

Primary hyperaldosteronism (Conn 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 potassium 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 sodium levels within the bloodstream. 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 disease). It causes dehydration, low blood pressure, high potassium (hyperkalaemia) and low sodium (hyponatraemia) in the blood.

Aldosterone and renin tests are commonly requested together. High blood pressure together with a low potassium concentration within the bloodstream usually leads the doctor to request these two tests. Aldosterone levels are sometimes used in people 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 summarised in the table earlier. High levels of serum and urine aldosterone, along with a low plasma renin, indicate primary hyperaldosteronism (Conn syndrome). Secondary hyperaldosteronism, on the other hand, is indicated by an increase in both aldosterone and renin.

A low aldosterone concentration is usually part of adrenal insufficiency (Addison disease). In infants with a condition called congenital adrenal hyperplasia (CAH), 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.

As some medicines can affect the aldosterone-renin ratio results your doctor will tell you if you should change your medications before testing. For example beta-blockers and ACE inhibitors should ideally be stopped 2 weeks prior to testing and Spironolactone and other diuretics should ideally be withheld for 6 weeks before testing. If it is necessary to maintain the control of high blood pressure your doctor will prescribe alternative antihypertensive medication that has lesser effects on the aldosterone and renin results. Do not stop taking any medications unless specially advised by your doctor.

Liquorice can mimic aldosterone properties and should be avoided for at least two weeks before the test. This refers only to the actual products of the liquorice plant (hard liquorice); most soft liquorice and other forms of liquorice confectionary sold in the UK do not actually contain the plant extract. Check the packages label if you are not certain, or bring a package with you to ask your doctor. Stress and strenuous exercise may also alter the results.