Aldosterone Blood Test: High, Low & the Renin Ratio

Aldosterone is a hormone made by your adrenal glands that controls the balance of sodium (salt), potassium, and — through that — your blood pressure. The key point up front: aldosterone is almost never read alone. It is interpreted together with renin, as the aldosterone-to-renin ratio (ARR), to screen for primary aldosteronism (also called Conn syndrome), the most common curable cause of secondary high blood pressure — and one of the most underdiagnosed. This guide covers normal aldosterone levels, what a high or low result means, and why the collection conditions matter so much. Aldosterone is part of a broader hormone panel.

Key takeaways

• Aldosterone is the body's main mineralocorticoid, made by the adrenal cortex; it makes the kidney retain sodium and excrete potassium, raising blood volume and blood pressure (the renin-angiotensin-aldosterone system, or RAAS).¹
• It is never interpreted in isolation — the aldosterone-to-renin ratio (ARR) is what guides diagnosis.¹²
• High aldosterone + low renin (high ARR) suggests primary aldosteronism (Conn syndrome); high aldosterone + high renin suggests a secondary cause (renal artery stenosis, heart failure, cirrhosis, diuretics).³⁴
• Primary aldosteronism likely causes at least 5–10% of all hypertension — probably more — yet fewer than 1% of people with high blood pressure are ever screened: a major public-health gap.⁵⁶⁷
• Levels depend heavily on posture, time of day, salt intake, and especially many medications (diuretics, spironolactone, ACE inhibitors/ARBs, beta-blockers), so the draw follows strict conditions.¹²
• High aldosterone is not a cancer marker: it speaks to blood pressure, salt, and potassium, not a malignant tumor.

What is aldosterone?

Aldosterone is a steroid hormone made by the outer layer (the zona glomerulosa) of the adrenal gland, which sits on top of each kidney. It is the body's main mineralocorticoid, and its job is to manage salt and water. It acts on the kidney to make it hold on to sodium (and therefore water) and to excrete potassium in the urine. By retaining water, it increases blood volume and, in turn, blood pressure.¹

Aldosterone is the final step in a cascade called the renin-angiotensin-aldosterone system (RAAS). When blood pressure drops or salt runs low, the kidney releases renin, an enzyme that triggers a chain reaction producing angiotensin II, which then stimulates the adrenal gland to make aldosterone. Blood potassium and the hormone ACTH also fine-tune its release. This system is the body's thermostat for salt and pressure — which is exactly why aldosterone and renin are read together.¹⁴

Aldosterone is not cortisol. Both come from the adrenal gland, but cortisol (the "stress hormone") is a glucocorticoid, while aldosterone is the mineralocorticoid of salt and water. This guide is about plasma aldosterone, measured in the blood, usually alongside renin.

Why the test is done

Aldosterone is not part of a routine blood panel. Your clinician orders it — almost always paired with renin — in targeted situations:¹⁸³

• high blood pressure that is hard to control, resistant to treatment, or diagnosed before age 40;
• hypertension with a low potassium (hypokalemia), either spontaneous or worsened by diuretics — the "classic" red flag;
• an adrenal nodule found by chance on imaging (an "incidentaloma");
• hypertension with obstructive sleep apnea, or a family history of early hypertension or stroke;
• less often, working up adrenal insufficiency (aldosterone would be low), an abnormal potassium, or an acid-base disturbance.

The main goal is to screen for primary aldosteronism: it is the most common potentially curable cause of secondary hypertension, and finding it allows targeted treatment (a specific medication or surgery) instead of just pushing on the blood-pressure numbers.⁹⁴⁸

Do you need to fast?

Strict fasting is not always required, but aldosterone is one of those tests where the collection conditions matter more than anything else. In practice the draw is usually done in the morning, after a few minutes seated (or following a specific lying-down/standing protocol set by the lab), on a normal salt intake and with potassium corrected first. Above all, several medications may need to be adjusted by your clinician before the test (see below). Follow your order's instructions exactly and report all your medications (see Do you need to fast before a blood test?).¹²

Normal ranges

Below are indicative adult reference values. They vary widely by lab, assay method, unit (ng/dL or pmol/L), and — above all — posture at the time of the draw. Always compare against the range printed on your report.¹⁰¹¹

Units: the common U.S. unit is ng/dL; to convert to SI, ng/dL × 27.7 ≈ pmol/L. Values rise on standing (simply getting up activates the RAAS) and are lower lying down. So it is not the single number that matters, but its ratio to renin (ARR) under standardized conditions.¹²

The aldosterone-to-renin ratio (ARR). This is the real screening tool. A high ARR — most often a normal-to-high aldosterone against a suppressed renin (for example a ratio above ~30 with aldosterone > 15 ng/dL, though cutoffs depend on the units and assay) — points toward primary aldosteronism and requires confirmatory testing before any diagnosis is made.¹³²

Understanding your results

Aldosterone is always read as a pair with renin. It is the combination of the two that carries meaning.

High aldosterone

A high aldosterone falls into two broad categories, which renin tells apart:³⁴

• High aldosterone + LOW renin (high ARR) → primary aldosteronism (Conn syndrome). The adrenal gland produces too much aldosterone on its own, most often from a benign adenoma (a small non-cancerous tumor) on one side, or from hyperplasia of both adrenals. The result is high blood pressure, sometimes with low potassium. This is the form not to miss, because it is curable — with a specific medication (a mineralocorticoid receptor antagonist) or, if only one side is responsible, by surgically removing the affected adrenal.⁴⁸
• High aldosterone + HIGH renin → secondary aldosteronism. Here the adrenal responds normally to an over-activated RAAS: renal artery stenosis, heart failure, cirrhosis, nephrotic syndrome, or diuretic use. Aldosterone is high, but for a "good reason" — the underlying cause is what needs treating, not the hormone.³

Always tie the result to your other markers: renin, potassium, and sodium, which complete the picture, and cortisol if a broader adrenal problem is suspected.

Low aldosterone

A low aldosterone points toward:¹

• adrenal insufficiency (for example Addison's disease), where the adrenal no longer makes enough hormones — often with a high potassium and low sodium;
• hypoaldosteronism (isolated, or linked to certain kidney conditions, diabetes, or medications such as ACE inhibitors/ARBs, NSAIDs, or heparin);
• more simply, the effect of a high-salt intake or of drugs that suppress the RAAS.

The cancer myth

A high aldosterone is not a sign of cancer. In the vast majority of primary aldosteronism, the cause is a benign adenoma or simple hyperplasia; adrenal cancer (adrenocortical carcinoma) is rare. Aldosterone reflects your blood pressure, salt, and potassium, not a malignant tumor — indeed, when adrenal imaging is requested, part of its job is to rule out that rare possibility.⁶

What affects your aldosterone

Few blood tests are as sensitive to conditions as aldosterone. The result can be shifted by:¹²

• posture (lying vs standing) and the time of day of the draw;
• salt intake (a very high-salt diet lowers aldosterone, a low-salt diet raises it) and your potassium level;
• many medications: spironolactone and eplerenone (mineralocorticoid receptor antagonists), diuretics, ACE inhibitors/ARBs, beta-blockers, NSAIDs, licorice… Some must be adjusted several weeks before the test, only on a clinician's decision — never stop a medication on your own;
• pregnancy (which physiologically raises aldosterone), stress, and exertion.

That's why a poorly prepared draw is uninterpretable: it is better to repeat the test under proper conditions than to conclude from a biased number.

Recent research

According to recent PubMed-indexed publications:

• An underdiagnosed giant. Multiple reviews note that primary aldosteronism is the most common endocrine cause of hypertension and is potentially curable, yet fewer than 1% of affected people are ever diagnosed — a striking gap between true prevalence and detection.⁶⁵ (Azizan et al., Nat Rev Nephrol, 2023 — DOI; Funder, Trends Cardiovasc Med, 2021 — DOI.)
• Toward broader screening. The new Endocrine Society guideline (2025) suggests screening every person with hypertension for primary aldosteronism by measuring aldosterone and renin and calculating the ARR, then letting the result guide care — a major shift from screening only "high-risk" groups.⁸ (Adler et al., J Clin Endocrinol Metab, 2025 — DOI.)
• A specific cardiovascular risk. Compared with "ordinary" hypertension at the same level, untreated primary aldosteronism carries an excess of cardiovascular events (atrial fibrillation, left-ventricular hypertrophy, stroke, kidney disease), which strengthens the case for early diagnosis and targeted treatment.⁴⁵
• Making the test reliable. Research stresses standardizing the ARR (choice of renin measure — activity vs concentration —, posture, potassium correction, and medication adjustments), because a poorly calibrated test is the leading source of false results and of patients "lost" at the very first screening step.²³

These findings concern diagnosis and research; they do not authorize self-medication and do not replace your physician's advice.

Get your aldosterone interpreted by AI DiagMe

An aldosterone level is never read alone: its meaning depends on your renin, your potassium, your sodium, your blood pressure, your posture at the draw, and your medications. That cross-reading — especially the aldosterone-to-renin ratio — is what gives the result its real value.

👉 AI DiagMe interprets your lab results — blood, urine, or stool — in plain language, taking your whole profile into account. An informational service that does not provide a diagnosis and complements, never replaces, your physician.

Frequently asked questions

The bottom line

Aldosterone is the hormone of salt, potassium, and blood pressure, made by the adrenal gland at the end of the renin-angiotensin-aldosterone system. The essential message: it is never read alone, but with renin, as the aldosterone-to-renin ratio. A high aldosterone with a low renin should prompt a search for primary aldosteronism (Conn syndrome) — the most common curable cause of secondary hypertension, and one that is badly underdiagnosed. Values depend on posture, salt, and medications, and vary by lab; this is not a cancer marker. No number is read in isolation — it's your whole set of markers and your context that counts, which is what AI DiagMe provides, alongside your physician.

Sources

Official sources and peer-reviewed publications (PubMed) used for this guide: