To see if your aldosterone or renin levels are abnormal; to detect hyperaldosteronism (overproduction of aldosterone) or hypoaldosteronism (underproduction of aldosterone)
Aldosterone and Renin
Your doctor may to take a blood sample for aldosterone and renin if you have high blood pressure which is sustained, may be difficult to control, possibly associated with a low blood potassium or have a family history of high blood pressure or early stroke (less than 40 years).
You may be asked to adhere to an unrestricted salt diet prior to the test or to temporarily discontinue one or more medications. The amount of salt in the diet and medicines, such as over-the-counter pain relievers can affect the test results. Medicines of the non-steroid class (such as Ibuprofen) and beta blockers can increase the ratio of aldosterone to renin giving a false positive, whereas diuretics (water pills),angiotensin-converting enzyme (ACE) inhibitors and calcium channel blockers can reduce the ratio giving a false negative result. Oral contraceptives can affect the test results by falsely raising the ratio but this depends on the assay method used for renin in the laboratory. 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. Your doctor will also want to know if your serum potassium level is low as this would affect the aldosterone level.
Please follow any instructions you are given, as this is important to ensure the validity of test results.
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 it used?
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
Disease Aldosterone Renin Cortisol Primary hyperaldosteronism High Low Normal Secondary hyperaldosteronism High High Normal Cushing syndrome Low-normal Low High Adrenal insufficiency (Addison disease) Low High Low
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.
When is it requested?
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.
What does the test result mean?
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.
Is there anything else I should know?
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.
Are there any other precautions I should take before the test?
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.
If my posture is important in the outcome of the results, how can I control it?
Are there any other conditions associated with abnormal aldosterone levels?
As well as medicines other conditions can affect aldosterone results. Pregnancy or renal impairment can result in higher aldosterone levels whereas Addison disease or advancing age can result in low aldosterone levels. Also aldosterone concentrations within the blood can fall to very low levels with severe illness, so testing should be done after recovery.