Aldosterone: Blood Pressure & Salt Balance

Aldosterone is a steroid hormone that helps the body manage sodium, potassium, and fluid, which in turn influences blood pressure. It works mainly on the kidneys and is a central part of the system that keeps salt and water balance steady.

What aldosterone is

Aldosterone belongs to a group of steroid hormones called mineralocorticoids, all built from cholesterol through a series of enzyme steps in the adrenal gland. As a steroid, it is fat-soluble and works by entering cells and switching certain genes on or off, which means its effects build over minutes to hours rather than instantly. Its primary job is to fine-tune how much sodium the body holds onto and how much potassium it lets go, which together set total fluid volume and help determine blood pressure.

Because salt and water balance touch so many systems, aldosterone links the kidneys, the blood vessels, and the heart into one coordinated effort to keep circulation stable. It is often described as the body's main "salt-retaining" hormone.

Where it is produced

Aldosterone is made in the adrenal glands, two small glands that sit like caps on top of the kidneys. Specifically, it is produced in the outermost layer of the adrenal cortex, a thin region called the zona glomerulosa. This zone is specialized for mineralocorticoid production and responds to a different set of signals than the deeper layers that make cortisol and adrenal androgens, which lets the body adjust salt balance somewhat independently of the stress steroid system.

What it does across body systems

• Sodium retention: It signals the kidneys to reabsorb sodium from the urine back into the bloodstream rather than letting it be lost.
• Potassium balance: As sodium is reclaimed, potassium is moved into the urine to be excreted, which helps keep blood potassium in a safe range.
• Fluid and blood pressure: Because water tends to follow sodium, holding onto sodium expands fluid volume and helps support blood pressure.
• Acid-base balance: It influences how the kidneys handle hydrogen ions, contributing to the body's overall acid-base balance.

Its main target is a particular part of the kidney's filtering tubes, but receptors for aldosterone are also present in the colon, sweat glands, and salivary glands, where it likewise nudges the body toward conserving sodium.

How levels are regulated

Aldosterone is governed largely by the renin-angiotensin-aldosterone system (RAAS), a cascade that protects blood pressure and salt balance. When blood pressure or sodium falls, or when the kidneys sense reduced blood flow, they release an enzyme called renin. Renin sets off a chain that converts an inactive precursor into angiotensin I and then into angiotensin II, a powerful signal that both narrows blood vessels and prompts the adrenal cortex to release aldosterone.

A second, more direct trigger is the potassium level in the blood: a rise in potassium stimulates aldosterone release on its own, which then helps shed the excess potassium. As sodium and fluid are restored and potassium returns to normal, renin output eases and the whole cascade settles — a feedback loop that keeps the system from overcorrecting. ACTH from the pituitary can give aldosterone a modest, short-lived nudge as well, but it is not the main controller.

Why testing conditions are standardized

Because posture, salt intake, time of day, and many medications all shift the RAAS, aldosterone is one of the most condition-sensitive hormones to measure. Standing up, for instance, activates the system and tends to raise aldosterone, while a high-salt diet suppresses it. This sensitivity is exactly why clinicians control the conditions of a blood draw and interpret aldosterone next to renin rather than on its own.

The logic of the aldosterone-to-renin ratio

Pairing aldosterone with renin is so useful because the two normally move together: when renin rises, it drives aldosterone up, and when renin falls, aldosterone should fall with it. By comparing them as a ratio, a clinician can ask a sharper question than either value alone allows — not simply "is aldosterone high?" but "is aldosterone high relative to the signal that is supposed to be driving it?" An aldosterone level that stays elevated while renin is low suggests the adrenal gland may be producing the hormone somewhat on its own, whereas aldosterone and renin rising together points to the cascade responding to something upstream, such as reduced blood flow to the kidneys. This is a clear illustration of why hormones are best read in context rather than as isolated numbers.

What high or low levels can be associated with

Persistently high aldosterone, often described as hyperaldosteronism, can be associated with elevated blood pressure and a tendency toward low blood potassium, because the body holds extra sodium and water while shedding potassium. Looking at aldosterone together with renin helps a clinician judge whether the adrenal gland is producing too much on its own or simply responding to a signal further upstream.

Low aldosterone can be associated with forms of adrenal insufficiency and with a tendency toward high blood potassium and low blood pressure, since the body cannot hold onto sodium as effectively. These associations are qualitative and always read in context alongside other measurements; see the conditions index and discuss concerns with a clinician.

How it is measured

Aldosterone is measured from a blood sample, frequently paired with a renin measurement so that the two can be compared as an aldosterone-to-renin ratio. Because posture and salt strongly affect the result, the draw is often standardized — for example, after the person has been upright or lying down for a set time, and sometimes after a defined salt intake. It is typically ordered as part of a broader evaluation rather than as a routine screen. See the blood tests overview and the glossary for related terms.

Relationships with other hormones

Aldosterone is the final step of the renin-angiotensin-aldosterone cascade, so it is read most meaningfully alongside renin and the blood electrolytes sodium and potassium. It is a close cousin of cortisol — both are adrenal steroids made from cholesterol — but the two are produced in different layers of the cortex and answer to different signals, which lets the body manage salt balance and stress somewhat separately. It also works in counterpoint to other fluid-balance signals, so a full picture usually means looking at several of these together. To explore the neighboring messengers, see the hormones index.