Conn's syndrome

Last Review Date: July 1, 2018

What is it?

Conn’s syndrome is another name for primary hyperaldosteronism, an endocrine disorder characterized by excessive secretion of the hormone aldosterone from the adrenal glands. This overproduction leads to the retention of sodium and loss of potassium in the body, resulting in high blood pressure (hypertension).  The adrenal glands are small triangular organs located on the top of the kidneys. They are part of the endocrine system, a group of glands that produce and secrete hormones that act on and regulate many systems throughout the body.

Aldosterone is a hormone that plays an important role in maintaining blood volume, pressure, and electrolyte balance. Its production is normally regulated by renin, an enzyme produced in the kidneys. When renin increases (due to low blood pressure, decreased blood flow to the kidneys or to a sodium deficiency), aldosterone increases; when renin decreases, aldosterone decreases.In Conn’s syndrome, an individual can produce excess aldosterone because of one or more benign adrenal tumors, by over activity of both glands called bilateral adrenal hyperplasia, or for unknown reasons (idiopathic). Rarely, it is caused by a cancerous (malignant) adrenal tumor. Regardless of the cause, aldosterone is produced despite low renin levels

Increased aldosterone can lead to hypokalaemia, increased blood pH (alkalosis), and high blood pressure. It may cause a few nonspecific symptoms such as  weakness, fatigue, and muscle cramps. A healthcare practitioner may suspect primary aldosteronism in a person who has high blood pressure that is difficult to control, requires multiple blood pressure medications, and/or does not respond to standard treatments.

The presence of hypokalaemia in a person with high blood pressure suggests the need to look for primary hyperaldosteronism although the most common cause of this pattern is as a side-effect of some of the drugs used to treat high blood pressure.

Diagnosing Conn’s syndrome is important because it represents one of the few causes of high blood pressure that is potentially curable. Although anyone can get primary hyperaldosteronism, it commonly occurs in adults between the ages of 30 and 50 and is more common in women than men. It can sometimes be difficult to diagnose as patients may have variable symptoms or no symptoms at all. Suspicion of Conn’s syndrome may be raised in patients who are resistant to the standard therapies used to treat high blood pressure.

Secondary aldosteronism, must be distinguished from primary aldosteronism. Secondary aldosteronism is caused by problems outside the adrenal glands that lead to the glands releasing too much aldosterone.It can occur as a result of anything that increases renin levels, such as decreased blood flow to the kidneys, low blood pressure, or low sodium levels in the urine. The most important cause is narrowing of the blood vessels that supply the kidney, termed renal artery stenosis. Other causes of secondary hyperaldosteronism include congestive heart failurecirrhosiskidney disease, and toxaemia of pregnancy.



The goal with testing for Conn’s syndrome is to identify primary hyperaldosteronism, distinguish between primary and secondary types, and distinguish between those types of primary hyperaldosteronism that may benefit from surgical intervention and those that will usually not.

Laboratory tests
Doctors will frequently order blood aldosterone and renin tests.  The ratio of aldosterone to renin is used to screen for primary hyperaldosteronism. If renin levels are low and aldosterone high, then the ratio will be significantly increased and primary hyperaldosteronism is likely to be present. Some medications can cause falsely negative or positive results and the doctor will decide if the tests need to be repeated after changing these medications. Based on the results of these tests, a doctor may do additional testing such as a suppresiion test, using sodium chloride or captopril administration, to see if aldosterone secretion decreases.

Electrolytes may be measured to look for an electrolyte imbalance – primarily decreased potassium and chloride but also increased bicarbonate. These tests may be followed by a CT (computed tomography) scan of the adrenal glands to look for a tumour. This process can be complicated as benign adrenal tumours are relatively common, especially as people get older. Many of them do not secrete aldosterone and are found during procedures for other reasons. Determining hyperplasia can also be tricky because the size of normal adrenal glands may vary significantly from one person to the next.

If hyperplasia or an aldosterone-producing tumour is suspected, but not easily locatable, then a doctor may order adrenal venous sampling. In this procedure, blood is collected from the vein that carries blood away from each adrenal gland. These blood samples are tested for aldosterone (sometimes cortisol is also measured and an aldosterone / cortisol ratio calculated) and then the results from the two adrenal glands compared. If they are significantly different, then it is likely that an adenoma is occurring in the gland with the highest aldosterone concentration. Adrenal venous sampling is performed only in hospital based specialised centres.

Non-laboratory tests

  • Blood pressure measurement - often the first indicator of possible primary hyperaldosteronism
  • CT (computed tomography) scan or MRI (magnetic resonance imaging) – used to locate adrenal tumours



The goals of treating Conn’s syndrome are to lower blood pressure to normal or near normal levels, decrease blood aldosterone levels, and resolve any electrolyte imbalance. The type(s) of treatment depend on the cause of the excess aldosterone secretion. If it is due to a single benign adrenal tumour, then the affected gland may be surgically removed. In many cases, this will completely resolve the high blood pressure and other associated symptoms, but in others some treatment will still be necessary to control blood pressure. If the primary hyperaldosteronism is due to a cancerous tumour (rare), then organs located next to the affected adrenal gland will need to be evaluated during surgery and more than the adrenal gland may need to be removed.

If the cause of the primary hyperaldosteronism cannot be determined (idiopathic) or appears to be due to hyperplasia in both adrenals, then surgery is usually not recommended. The patient’s condition will be treated with spironolactone (which blocks the action of aldosterone) and one or more blood pressure drug therapies.

Patients should consult with their doctors and, when indicated, with an endocrinologist (a specialist in the endocrine system). Treatment for primary hyperaldosteronism must often be adjusted to accommodate underlying high blood pressure, kidney disease, congestive heart failure, and a variety of other disorders.

Related pages

On this site
Tests: Aldosterone and renin, electrolytes, potassium
Conditions: Endocrine system and syndromes, hypertension

Elsewhere on the web
MedlinePlus Medical Encyclopedia: Hyperaldosteronism - primary and secondary
Mayo Clinic: Primary aldosteronism
Society for Endocrinology: You and Your Hormones - Hyperaldosteronism