Aldosterone and Renin

These tests require careful preparation because many factors can affect the results. Your doctor will give you specific instructions, which are very important to follow.

Medications

Many blood pressure medications affect aldosterone and renin levels. Your doctor may ask you to stop certain medications before testing but never stop any medication without your doctor’s advice.

Medications that can affect results include:

• Beta-blockers and ACE inhibitors: should ideally be stopped 2 weeks before testing
• Spironolactone and other diuretics (water tablets): should ideally be stopped 6 weeks before testing
• Non-steroidal anti-inflammatory drugs (NSAIDs): like ibuprofen – can cause false positive results
• Oral contraceptives: can affect results depending on the laboratory test method

Your doctor may prescribe alternative blood pressure medication during the preparation period to keep your blood pressure controlled.

Diet and lifestyle

• Salt intake: you may be asked to maintain an unrestricted (normal) salt diet
• Liquorice: avoid real liquorice products for at least 2 weeks before testing (most UK liquorice sweets don’t contain actual liquorice plant extract – check labels)
• Exercise: avoid strenuous exercise before the test
• Stress: try to be relaxed during testing as stress can affect results

Your doctor will also want to know if you have low potassium levels, as this affects aldosterone.

Sample collection

A blood sample will be taken from a vein in your arm, usually after a short period of rest in a seated position because standing or walking prior to the test may affect results. 

What the test measures

Aldosterone and renin are two hormones that work together as part of a complex system controlling blood pressure, blood volume, and the balance of sodium and potassium in your body.

Aldosterone

Aldosterone is a hormone made by the adrenal glands (small glands sitting on top of your kidneys). It tells your kidneys to:

• Keep (reabsorb) sodium and water
• Remove potassium

This helps control blood pressure – keeping sodium and water increases blood volume and raises blood pressure.

Renin

Renin is an enzyme produced by the kidneys. It starts a chain reaction that ultimately controls aldosterone production:

1. Kidneys release renin
2. Renin converts a protein in blood into angiotensin I
3. Angiotensin I is converted to angiotensin II
4. Angiotensin II signals the adrenal glands to release aldosterone

Normally, when renin increases, aldosterone increases. When renin is low, aldosterone decreases. The aldosterone-renin ratio helps identify when this normal relationship is disrupted.

Your doctor will look at both aldosterone and renin levels together, often along with cortisol. Different patterns point to different conditions.

Primary hyperaldosteronism (Conn’s syndrome)

Pattern: high aldosterone, low renin, normal cortisol

This condition is caused by overproduction of aldosterone by the adrenal glands, usually due to a benign tumour in one gland or overgrowth of both glands. The excess aldosterone causes the kidneys to retain too much sodium and water whilst losing potassium.

This leads to:

• High blood pressure
• Low potassium levels (which can cause muscle weakness)
• High sodium levels

Secondary hyperaldosteronism

Pattern: high aldosterone, high renin, normal cortisol

This occurs when something outside the adrenal glands triggers excessive renin production, which then drives up aldosterone. The kidneys produce more renin in response to reduced blood flow, low blood pressure, or low sodium.

Common causes include:

• Renal artery stenosis: narrowing of the arteries supplying the kidneys (most important cause)
• Heart failure
• Liver cirrhosis
• Kidney disease
• Pre-eclampsia in pregnancy

Cushing’s syndrome

Pattern: low-normal aldosterone, low renin, high cortisol

High cortisol levels suppress both aldosterone and renin. Cushing’s syndrome is caused by prolonged exposure to high cortisol levels, either from medication or from tumours producing excess cortisol.

Adrenal insufficiency (Addison’s disease)

Pattern: low aldosterone, high renin, low cortisol

The adrenal glands are damaged and cannot produce enough hormones, including aldosterone and cortisol. The body tries to compensate by producing more renin.

This causes:

• Dehydration
• Low blood pressure
• High potassium (hyperkalaemia)

Low sodium (hyponatraemia)

If primary hyperaldosteronism is suspected

A high aldosterone-renin ratio suggests primary hyperaldosteronism (Conn’s syndrome). Your doctor will request further tests to confirm this and identify the cause.

Confirmatory tests:

• Salt loading test or fludrocortisone suppression test
• 24-hour urine aldosterone

Locating the source:

• CT or MRI scan of adrenal glands
• Adrenal vein sampling (inserting a catheter to collect blood directly from adrenal veins to see which side is producing excess aldosterone)

Treatment options:

• If one adrenal gland: surgical removal (adrenalectomy) – this can cure high blood pressure
• If both glands: medication (spironolactone or eplerenone) to block aldosterone’s effects

If secondary hyperaldosteronism is suspected

Your doctor will investigate what’s triggering the excess renin and aldosterone production.

Tests to identify the cause:

• Kidney ultrasound or CT/MRI angiography (to check for renal artery stenosis)
• Renal vein renin sampling (catheter procedure to measure renin from each kidney separately)
• Heart function tests (if heart failure suspected)
• Liver function tests (if cirrhosis suspected)

Treatment: depends on the underlying cause. For renal artery stenosis, treatment might include angioplasty (opening the narrowed artery) or surgery.

If adrenal insufficiency is suspected

Additional tests:

• Synacthen test (tests adrenal gland response)
• Morning cortisol
• ACTH levels
• Adrenal antibodies

Treatment: hormone replacement therapy with hydrocortisone and fludrocortisone (replaces missing cortisol and aldosterone).

Using results to guide treatment

Some doctors use aldosterone and renin levels to help select the most effective blood pressure medications for individual patients. Different patterns respond better to different medication types.

Many factors can affect aldosterone and renin levels, which is why careful preparation is essential.

Medications:

• Beta-blockers and NSAIDs (like ibuprofen) → can falsely increase the aldosterone-renin ratio
• Diuretics, ACE inhibitors, calcium channel blockers → can falsely decrease the ratio
• Oral contraceptives → can affect results depending on laboratory method

Diet:

• Salt intake affects both hormones
• Real liquorice mimics aldosterone effects

Physical factors:

• Stress
• Strenuous exercise

Other conditions:

• Pregnancy (increases aldosterone)
• Kidney impairment
• Advancing age (decreases aldosterone)
• Low potassium levels (affect aldosterone)
• Severe illness (aldosterone falls to very low levels – testing should wait until recovery)

Aldosterone and renin testing is usually part of a broader investigation. Your doctor will typically request other tests alongside these.

Electrolyte tests:

• Sodium – often high in primary hyperaldosteronism
• Potassium – often low in primary hyperaldosteronism, high in adrenal insufficiency

Other hormone tests:

• Cortisol (helps distinguish different conditions)
• ACTH
• Synacthen test

Imaging:

• CT or MRI of adrenal glands
• Kidney imaging (ultrasound, CT, MRI)
• Renal angiography (to look for artery narrowing)

Specialized procedures:

• Adrenal vein sampling
• Renal vein renin sampling

The renin-angiotensin-aldosterone system (RAAS) is one of the body’s main blood pressure control mechanisms. It works like a thermostat, constantly adjusting to maintain proper blood pressure and electrolyte balance.

When blood pressure drops or sodium levels fall, the kidneys detect this and release renin. This triggers a cascade of events leading to aldosterone release, which brings blood pressure back up.

When blood pressure is too high or sodium levels are too high, this system should switch off – renin decreases and aldosterone decreases.

In primary hyperaldosteronism, this feedback system is broken. The adrenal glands produce aldosterone regardless of what renin is doing, leading to high blood pressure that’s difficult to control.

Many blood pressure medications work by targeting different parts of this system. ACE inhibitors block the conversion of angiotensin I to angiotensin II. Angiotensin receptor blockers (ARBs) stop angiotensin II from working. Aldosterone antagonists (like spironolactone) block aldosterone’s effects on the kidneys.