Primary Aldosteronism (Conn's Syndrome)

Primary aldosteronism, sometimes called Conn's syndrome, is a condition in which the adrenal glands make too much of the hormone aldosterone. Because aldosterone controls how the body handles salt and water, the result is often raised blood pressure that can be difficult to control. It is one of the more common hormonal causes of high blood pressure and is identified through specific blood tests.

What primary aldosteronism is

The two adrenal glands sit on top of the kidneys and release several hormones, including aldosterone. Aldosterone acts on the kidneys to retain sodium and water and to excrete potassium, which helps regulate blood volume and blood pressure. In primary aldosteronism, one or both adrenal glands produce aldosterone in excess and in a way that no longer responds normally to the body's usual controls.

The word "primary" means the problem lies within the adrenal glands themselves, rather than being a response to a signal from elsewhere. Normally, aldosterone release is governed by a system that links the kidneys, the hormone renin, and a chain of signals known as the renin-angiotensin-aldosterone pathway. When blood pressure or blood volume falls, the kidneys release more renin, which leads to more aldosterone; when blood pressure is adequate, renin and aldosterone settle back down. In primary aldosteronism this feedback loop is uncoupled: the adrenal glands keep producing aldosterone regardless of the body's needs, while renin is typically suppressed to low levels.

The excess aldosterone leads the body to hold on to too much salt and water and to lose potassium. Over time this tends to raise blood pressure, and in some people it lowers the blood potassium level. Recognising the condition matters because it can be managed more specifically than high blood pressure of unknown cause, and because long-standing aldosterone excess may affect the heart, blood vessels, and kidneys beyond what blood pressure alone would explain.

How it differs from ordinary high blood pressure

Most high blood pressure has no single identifiable cause and is described as primary or essential hypertension. Primary aldosteronism is a distinct, hormone-driven cause that can sometimes be traced to a specific gland and, in certain cases, addressed at its source. This is why clinicians may look for it rather than assuming all raised blood pressure is the same.

Common signs and symptoms

Many people with primary aldosteronism have few specific symptoms, and the condition is often suspected because blood pressure is high and hard to control. When symptoms do occur, they frequently reflect raised blood pressure or a low potassium level and may include:

• High blood pressure, sometimes needing several medicines
• Headaches
• Muscle weakness, cramps, or spasms
• Tiredness or low energy
• Increased thirst and frequent urination
• Tingling or numbness in some cases
• Palpitations, which can accompany a low potassium level

Because these features are mild or absent in many people, the condition can go unrecognised for a long time. It is often the pattern of the blood pressure — high, persistent, and not easily controlled — rather than a dramatic symptom that prompts testing.

What causes it

Primary aldosteronism usually arises from one of two patterns within the adrenal glands. In one, a single benign growth on one gland, called an aldosterone-producing adenoma, produces excess aldosterone. In the other, both glands are diffusely overactive, a pattern often described as bilateral adrenal hyperplasia. Less common causes include certain inherited forms that can run in families, sometimes appearing at a younger age, and, rarely, an adrenal cancer. Distinguishing between a one-sided and a two-sided source is an important part of the evaluation because it strongly influences how the condition is managed.

How it is diagnosed

Diagnosis begins with screening blood tests and, when needed, moves to confirmatory testing and imaging. Because medicines, posture, salt intake, and the time of day can affect the results, testing is planned carefully by a clinician, who may adjust certain medications beforehand. Common steps include:

• Aldosterone and renin — these two are measured together, often as a ratio (the aldosterone-to-renin ratio), because their relationship helps reveal whether aldosterone is inappropriately high while renin is suppressed.
• Blood potassium and sodium — potassium is sometimes low, though it can be normal; sodium may sit toward the higher end.
• Confirmatory tests — further blood or salt-loading tests may be used to confirm the diagnosis after an abnormal screen, by checking whether aldosterone fails to fall as it normally should.
• Adrenal imaging — a scan, usually a CT of the adrenal glands, can look for a growth and assess the glands' appearance.
• Adrenal vein sampling — in some cases this specialised test compares hormone levels from each gland to clarify whether one or both are responsible.

The table below summarises the typical pattern clinicians look for. It is illustrative only; actual reference ranges vary by laboratory, posture, medication, and the way a sample is collected, so results must be interpreted by a clinician.

For background on the markers themselves, see our blood tests and hormones sections, and our conditions overview for related adrenal topics such as pheochromocytoma.

How it is generally managed

Management depends on whether one gland or both are overactive and is decided together with a clinician. When a single overactive gland is the source, surgery to remove that gland is one option that may improve blood pressure and potassium levels, and in some people reduce the number of medicines needed. When both glands are involved, medicines that block the effect of aldosterone are commonly used instead, often alongside other blood-pressure measures. Lifestyle factors such as salt intake may also be addressed as part of overall blood-pressure care. General treatment principles are outlined in our treatments section. This page is educational and does not describe doses; it is not a substitute for personalised medical advice.

Possible complications and when to seek care

Left unrecognised, the combination of raised blood pressure and the direct effects of excess aldosterone may, over time, place extra strain on the heart, blood vessels, and kidneys. A very low potassium level can also cause marked muscle weakness or disturbances of heart rhythm. For these reasons, blood pressure that is high and difficult to control, or that occurs with persistent muscle weakness, is worth discussing with a clinician. Sudden severe symptoms such as chest pain, fainting, or a markedly irregular heartbeat are reasons to seek urgent medical attention.

Living with primary aldosteronism

For many people, identifying primary aldosteronism brings the advantage of a more targeted approach to blood pressure than would otherwise be possible. After surgery or with ongoing medication, regular follow-up is usual to check blood pressure, potassium, and kidney function, and to review treatment over time. Keeping a record of blood-pressure readings, attending review appointments, and discussing any new symptoms all help a clinician fine-tune care. Where an inherited form is suspected, relatives may also be offered assessment.