Aldosterone Blood Test

What Does This Test Measure?

Aldosterone is a steroid hormone from the outer layer of the adrenal glands. It acts on the kidney to retain sodium and water and to excrete potassium. Because sodium retention pulls water with it, aldosterone is one of the principal regulators of blood volume and therefore blood pressure.

Its release is controlled mainly by the renin–angiotensin system rather than by ACTH. When blood pressure or sodium delivery to the kidney falls, the kidney releases renin, which sets off a cascade ending in aldosterone release. Potassium also stimulates it directly.

This is why aldosterone is almost always measured alongside renin, and why the aldosterone-to-renin ratio is the number that actually gets interpreted. A high aldosterone with high renin is a normal system responding to a stimulus; a high aldosterone with suppressed renin means the adrenal is acting on its own.

Why Your Doctor Ordered This Test

The main reason is high blood pressure that is difficult to explain or difficult to control, particularly hypertension needing three or more drugs, hypertension appearing before the age of 40, or hypertension accompanied by an unexplained low potassium.

Primary aldosteronism was long considered rare and is now recognised as one of the commonest identifiable causes of hypertension, so testing has become considerably more routine. Aldosterone is also measured when investigating adrenal masses, unexplained potassium abnormalities, or suspected adrenal insufficiency.

What High Aldosterone Means

High aldosterone with suppressed renin is primary aldosteronism, meaning the adrenal is producing hormone autonomously. The two usual forms are a single benign adenoma and bilateral overgrowth of both glands, and the distinction matters because the first can be cured surgically while the second is treated with medication. The classic picture is hypertension with a low potassium, though most people now diagnosed have entirely normal potassium.

High aldosterone with high renin is secondary and the gland is responding appropriately to a genuine signal. Causes include heart failure, cirrhosis with fluid retention, nephrotic syndrome, dehydration, diuretic treatment and narrowing of a renal artery. Here the aldosterone is a symptom of the underlying problem, not the problem itself.

What Low Aldosterone Means

Low aldosterone with low cortisol and a high ACTH indicates primary adrenal insufficiency, where the whole adrenal cortex has failed. Loss of aldosterone is what produces the low sodium, high potassium and low blood pressure that make Addison's disease dangerous.

Isolated low aldosterone with normal cortisol is less common and points to hyporeninemic hypoaldosteronism, seen particularly in diabetes with kidney involvement, where it causes a persistent high potassium and a mild acidosis. Several medications suppress aldosterone directly, including ACE inhibitors, angiotensin receptor blockers, spironolactone, eplerenone and NSAIDs, and these are a far more frequent explanation than adrenal disease.

How to Prepare and What Affects the Result

Preparation matters more here than for most tests, and getting it wrong is the usual reason results are uninterpretable. Potassium should be corrected before testing, since a low potassium suppresses aldosterone and can hide the diagnosis. Salt intake should be unrestricted in the days beforehand.

Several drugs must usually be stopped in advance under medical supervision: spironolactone and eplerenone for four to six weeks, and often diuretics, beta blockers, ACE inhibitors and angiotensin receptor blockers for two weeks, with safer alternatives substituted. Samples are typically taken mid-morning after the patient has been upright for at least two hours, with renin drawn at the same time. Liquorice, in confectionery or herbal preparations, mimics aldosterone and should be avoided.

Common Misinterpretations

The most consequential error is interpreting aldosterone without renin. The same aldosterone value means opposite things depending on whether renin is suppressed or raised, and the ratio is what distinguishes autonomous production from an appropriate response.

The second is testing without stopping interfering medication, which produces results that cannot be acted on and often leads to the diagnosis being wrongly excluded.

The third is assuming normal potassium rules out primary aldosteronism. It does not. The majority of people now diagnosed have normal potassium, and waiting for a low potassium before testing misses most cases.

Frequently Asked Questions

Why is aldosterone always measured with renin?

Because the ratio between them locates the problem. Aldosterone high with renin suppressed means the adrenal gland is producing hormone autonomously, which is primary aldosteronism. Aldosterone high with renin also high means the gland is responding correctly to something else, such as heart failure, dehydration or a narrowed renal artery. The aldosterone value alone cannot separate these.

Do I need to stop my blood pressure medication before this test?

Often yes, but only under medical supervision. Spironolactone and eplerenone usually need four to six weeks off, and diuretics, beta blockers, ACE inhibitors and ARBs are commonly paused for around two weeks with safer alternatives substituted. Never stop blood pressure treatment on your own; the substitution needs to be planned by whoever ordered the test.

Can I have primary aldosteronism with normal potassium?

Yes, and most people diagnosed today do. The textbook association with low potassium comes from an era when only severe cases were identified. Waiting for a low potassium before testing misses the majority of cases, which is why testing is now recommended based on the blood pressure pattern alone.

Does liquorice really affect this test?

It does. Liquorice contains glycyrrhizin, which blocks the enzyme that normally protects the kidney's mineralocorticoid receptor, producing an effect that closely imitates excess aldosterone, high blood pressure and low potassium, but with aldosterone itself suppressed. Regular consumption of liquorice sweets or herbal preparations should be stopped before testing and mentioned to your doctor.

Why does posture change the result?

Standing reduces effective blood volume reaching the kidney, which activates renin and raises aldosterone. Upright and lying values differ substantially, so results are only comparable when collection conditions match. Samples are usually taken mid-morning after at least two hours upright.

Related Markers: Read Together for Full Context

BloodWorker reads lab values together, not in isolation. These related markers provide essential context for interpreting your Aldosterone result: