• Aldosterone and renin are hormones that are important for managing your blood pressure.
• Your kidneys help control your blood pressure and aldosterone helps them hold on to salt (sodium) to raise blood pressure while getting rid of potassium which lowers blood pressure.
• Aldosterone is made by your adrenal glands.
• Renin is made by your kidneys and released when your body senses low blood pressure, low sodium levels or stress. It triggers a chain reaction that leads to the release of aldosterone from your adrenal glands.
• If your adrenal glands make too much aldosterone, keeping your blood pressure too high, you are said to have aldosteronism.
• The aldosterone/renin ratio (ARR) is a screening test used to check whether high blood pressure may be caused by excess aldosterone.

If you have high blood pressure that is not responding to standard medications your doctors may suggest tests for aldosterone and renin.

Blood takes oxygen and nutrients to all parts of your body. Your beating heart helps to push blood through a network of blood vessels – arteries and veins. Your blood vessels are constantly adjusting, contracting or relaxing, becoming narrower or wider to keep your blood pressure stable and blood flowing.

Your blood pressure goes up and down in response to things like exercise, eating, stress, medications and underlying health conditions. Problems arise if your blood pressure stays too high for too long.

High blood pressure, called hypertension, makes your heart work harder than normal and over time this weakens the heart muscle. The increased pressure of blood flow can damage your blood vessels, making them stiff or narrower and this increases the risk of blood clots.
Blood pressure is the measure of the force of your blood as it pushes against the walls of your arteries.

• Systolic pressure - the force when your heart beats.
• Diastolic pressure - the force when your heart rests between beats.

How your kidneys help control blood pressure
Your kidneys are located just at the bottom of your ribcage on either side of your spine. Inside each kidney are about a million tiny blood filtering units. These filter your blood and remove waste and excess water from your body. Water is sent to your bladder to be removed as urine.

When your kidneys filter out water from your blood, the amount of water that is kept in your bloodstream and the amount that is passed into your urine to be removed can be adjusted.

• When your blood pressure is too low, your kidneys sense this and they allow more fluid to return to your bloodstream to increase blood volume. When blood volume is raised and more is being pumped through the system, your blood pressure goes up.
• When your blood pressure is too high, your kidneys sense this and remove fluid from your bloodstream to reduce blood volume. When blood volume is reduced your blood pressure goes down.
• As well as increasing or lowering blood volume, your blood vessels contract and relax to keep blood pressure in balance.
• They relax (widen) to let blood flow through more easily and lower blood pressure or contract (narrow) to force blood through and raise pressure.

Sodium

Your kidneys use sodium as a way of controlling how much water stays in your blood and therefore, how much blood volume and blood pressure you have.

The kidneys’ tiny filters pull sodium out of the urine and into the bloodstream. Water naturally moves towards areas where there is sodium in a process called osmosis. When sodium moves back into the blood, water follows. This extra water increases blood volume and raises blood pressure. For more see Sodium.

Potassium

The electrolyte potassium works in the opposite way to sodium, and it helps the kidneys get rid of excess sodium from your bloodstream through your urine. Potassium also directly affects your blood vessels. It causes them to relax and widen making it easier for blood to flow lowering blood pressure. For more see Potassium.

Aldosterone

Aldosterone is a hormone that helps the body to maintain normal blood pressure. It does this by enabling the kidneys to hold on to salt (sodium) while getting rid of potassium which is passed into the urine.

Aldosterone is made by the adrenal glands which sit on top of the kidneys, and the amount that is produced is controlled by renin, an enzyme made by the kidneys.

How aldosterone and renin help control blood pressure

The renin-angiotensin-aldosterone system (RAAS) is a complex feedback system of hormones, enzymes and proteins that helps control your blood pressure.

1. When your kidneys sense low blood pressure, certain cells in the kidneys release renin into your bloodstream. This sets off a chain reaction that stimulates your adrenal glands to release aldosterone.
2. Aldosterone helps your kidneys hold on to sodium. Because sodium attracts water this increases water retention.
3. Water raises blood volume and therefore blood pressure, bringing the system back into balance.
4. Once your blood pressure and blood volume return to normal, your kidneys release less renin, completing the feedback loop.

Blood tests for both aldosterone and renin are often ordered if you have high blood pressure and test results show you also have a low potassium level. Even if potassium is normal, testing may be done if typical medications are not controlling your high blood pressure or if you have had high blood pressure from an early age. Sometimes aldosterone and renin testing is used to clarify the best treatment for high blood pressure.

Primary aldosteronism
Up to 20 percent of people with resistant high blood pressure have a condition known as primary aldosteronism. This is when they have high levels of aldosterone in their blood due to problems with their adrenal glands. One or both adrenal glands make too much aldosterone which leads to too much salt and water being retained in the body, causing high blood pressure. In some people this can also lead to low blood potassium levels.

About 30 – 40 percent of primary aldosteronism cases are caused by benign (non-cancerous) adrenal tumours. This is known as Conn’s syndrome. About 60 – 70 percent are due to both adrenal glands being overactive in a condition called bilateral adrenal hyperplasia. There are other less common causes and rarely, it is caused by cancer of the adrenal gland. There are hereditary types of primary aldosteronism, but these are also rare and most often seen in people younger than 20 years with a family history of stroke and hypertension.

Secondary aldosteronism

Unlike primary aldosteronism, secondary aldosteronism is caused by problems outside the adrenal glands. This can be caused by a range of different health disorders. It is very common in congestive heart failure and almost all cases of cirrhosis of the liver with ascites. In these cases, the reduced blood flow to the kidneys causes more renin to be released, which increases the production of aldosterone. It is also common in chronic kidney disease, renal artery stenosis (narrowing of one or both arteries that carry blood to the kidneys) and pre-eclampsia in pregnancy. Secondary aldosteronism is more common than primary aldosteronism and your treatment will be different.

Diagnosing aldosteronism is important because it represents one of the few causes of high blood pressure that is potentially curable. It can sometimes be difficult to diagnose because many people only have vague symptoms or no symptoms at all. This means the condition can go unnoticed unless specific testing is done.

Hypoaldosteronism

A lack of aldosterone, called hypoaldosteronism, usually occurs as part of adrenal insufficiency (Addison's disease). It causes dehydration, low blood pressure, hyperkalaemia (high potassium), hyponatraemia (low sodium) and skin pigmentation.

Aldosterone testing, along with other tests, may be requested if your doctor suspects that you have a condition called adrenal insufficiency, known as Addison’s disease. Aldosterone testing can support this diagnosis, but cortisol and ACTH tests are the main tests used to diagnose Addison’s disease.

Primary hyperaldosteronism and the aldosterone–renin ratio (ARR)

A calculation called the aldosterone–renin ratio (ARR) is used to screen for primary aldosteronism. This compares the level of aldosterone with renin. Normally, if renin levels go up, aldosterone levels also go up. If renin levels go down, aldosterone levels go down. However, if you have primary aldosteronism this normal relationship is disrupted and your aldosterone will be high, but your renin level will be low. Renin is said to be suppressed.

When aldosterone is high and renin is low, the ARR ratio becomes higher. A high ARR result suggests you have primary aldosteronism, but further tests are needed to confirm the diagnosis.

Sample

Blood.

Any preparation?

Providing a blood sample for aldosterone testing needs careful preparation because aldosterone levels are very sensitive to posture, salt intake, time of day and medications. Both aldosterone and renin are highest in the morning and vary throughout the day.

Blood is collected in the morning, at least two hours after getting out of bed. You may be asked to arrive well before your testing time and be asked to sit, stand or lie down for a period of time before the blood sample is collected.

The amount of salt in your diet and medications, such as anti-inflammatory drugs (ibuprofen) diuretics (water pills), beta blockers, steroids, some blood pressure medications and oral contraceptives, can affect the test results. Do not stop any medication unless your doctor tells you to. Stress and strenuous exercise may also alter the results.

Your doctor will tell you if you should change the amount of salt in your diet, your medications or your exercise routine before aldosterone testing.

Aldosterone levels fall to very low levels in severe illness, so testing should not be done when a person is very ill.

Liquorice may mimic aldosterone's properties and should be avoided for at least two weeks before the test. This refers only to products made from the extract of the liquorice root. Most liquorice sold in Australia is flavoured confectionary and does not contain liquorice, but some products do. Check the package label if you are not certain or bring a package with you to ask your doctor.

Reading your test report

Your results will be presented along with those of your other tests on the same form. You will see separate columns or lines for each of these tests.

• High aldosterone with low renin suggests primary aldosteronism (Conn’s syndrome). This produces a high ARR, which is why ARR is used as the main screening test.
• High aldosterone with high renin suggests secondary aldosteronism, where the adrenal glands are responding normally to signals from the kidneys. The ARR is normal or low.
• Infants with a condition called congenital adrenal hyperplasia (CAH) lack an enzyme needed to make cortisol. In some cases, this also decreases production of aldosterone. This is a rare cause of low aldosterone.

Reference intervals - comparing your results to the healthy population

Your results will be compared to reference intervals (sometimes called a normal range).

• Reference intervals are the range of results expected in healthy people.
• They are used to provide a benchmark for interpreting a patient's test results.
• When compared against them, your results may be flagged high or low if they sit outside this range.
• Some reference intervals are harmonised or standardised, which means all labs in Australia use them.
• Others are not because for these tests, labs are using different instruments and chemical processes to analyse samples.
• Always compare your lab results to the reference interval provided on the same report.

If your results are flagged as high or low this does not necessarily mean that anything is wrong. It depends on your personal situation.
Reference intervals for aldosterone and renin vary between laboratories so you will need to go through your results with your doctor, who will interpret the results based on the reference intervals provided by the laboratory.

Further testing

If your results show primary hyperaldosteronism, you may need more tests to confirm the diagnosis.

Aldosterone Suppression Test

A saline infusion test can be used to see if the aldosterone levels fall when your body levels of salt are high.

• In someone who does not have primary aldosteronism, saline causes aldosterone levels to drop, because the body senses extra fluid and sodium.
• In someone with primary aldosteronism, aldosterone stays high despite the fluid load.

CT scan

This will look at the size and shape of your adrenal glands to help identify the cause of your high aldosterone levels.

Adrenal venous sampling

Looking for cell changes and thickening of the adrenal glands (hyperplasia) can be tricky because the size of normal adrenal glands can vary significantly from one person to another. If adrenal hyperplasia is suspected, you may be asked to have adrenal venous sampling. This is a specialised test done by an experienced radiologist. It helps determine whether one or both adrenal glands are producing too much aldosterone.

The choice of tests your doctor makes will be based on your medical history and symptoms. It is important that you tell them everything you think may help.

You play a central role in making sure your test results are accurate. Do everything you can to make sure the information you provide is correct and follow instructions closely.

Talk to your doctor about any medications you are taking. Find out if you need to fast or stop any particular foods or supplements. These may affect your results. Ask:

• Why does this test need to be done?
• Do I need to prepare (such as fast or avoid medications) for the sample collection?
• Will an abnormal result mean I need further tests?
• How could it change the course of my care?
• What will happen next, after the test?

Pathology and diagnostic imaging reports can be added to your My Health Record. You and your healthcare provider can now access your results whenever and wherever needed.

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