Although some doctors measure either plasma or urine aldosterone by itself, in most cases it is necessary to measure both renin and aldosterone (and occasionally cortisol) to get a complete picture of what is happening with hormone production. These tests may be ordered to help diagnose and to monitor conditions associated with aldosterone excess or deficiency. The table below indicates the changes in renin, aldosterone, and cortisol that occur with different disorders. 
 

Disorder	Aldosterone	Cortisol	Renin
Primary hyperaldosteronism (Conn’s syndrome)	High	Normal	Low
Secondary hyperaldosteronism	High	Normal	High
Cushing’s syndrome	Low-normal	High	Low
Adrenal insufficiency (Addison's disease)	Low	Low	High
Pituitary disease	Normal	Low	Normal

Primary hyperaldosteronism is caused by the overproduction of aldosterone by the adrenal glands, usually by a benign tumor of one of the glands. The high aldosterone level increases reabsorption of sodium (salt) and loss of potassium by the kidneys, resulting in an electrolyte imbalance. Primary hyperaldosteronism is sometimes called Conn's syndrome. Symptoms are not typically present, although muscle weakness can occur if potassium levels are very low. The presence of hypokalemia in a person with hypertension suggests the need to look for hyperaldosteronism.

Secondary hyperaldosteronism, which is more common, can occur as a result of anything that decreases blood flow to the kidneys, decreases blood pressure, or lowers sodium levels. The most important cause is narrowing of the blood vessels that supply the kidney, termed renal artery stenosis. This causes high blood pressure due to high renin and aldosterone, that may be cured by surgery or angioplasty. Sometimes, to see if only one kidney is affected, a catheter is inserted through the groin and blood is collected directly from the veins draining the kidney (renal vein renin levels); if the value is significantly higher in one side, this indicates where the narrowing of the artery is present. Similarly, blood may sometimes be taken from both of the adrenal veins to determine whether there is a difference in the amount of aldosterone (and sometimes cortisol) produced by each of the adrenal glands. Secondary hyperaldosteronism may also be seen with congestive heart failure, cirrhosis, kidney disease, and toxemia of pregnancy.

Hypoaldosteronism (decreased production) usually occurs as part of adrenal insufficiency; it causes dehydration, low blood pressure, hyperkalemia, and hyponatremia.

A plasma and/or 24-hour urine aldosterone and a plasma renin may be ordered when a patient has high blood pressure and a low potassium. Aldosterone levels are sometimes ordered, along with other tests, when a doctor suspects that a patient has adrenal insufficiency. Since primary aldosteronism is a potentially curable cause of hypertension, and because it is often resistant to conventional treatment for high blood pressure, some doctors order aldosterone and renin levels when they want to help clarify the treatments that are likely to be effective in patients with high blood pressure.

The changes in plasma aldosterone, cortisol, and renin are summarized in the table earlier on the page. High levels of serum and urine aldosterone, along with a low plasma renin, indicate primary aldosteronism. Secondary aldosteronism, on the other hand, is characterized by an increase in both aldosterone and renin.

A low aldosterone is usually part of adrenal insufficiency or Addison's disease. In infants with congenital adrenal hyperplasia, the infant lacks an enzyme needed to make cortisol; in some cases, this also decreases production of aldosterone. This is a rare cause of low aldosterone.

The amount of salt in the diet and medications, such as over-the-counter pain relievers of the non-steroid class (such as Motrin and Advil), diuretics (water pills), beta blockers, steroids, angiotensin-converting enzyme (ACE) inhibitors, and oral contraceptives can affect the test results. Many of these drugs are used to treat high blood pressure. Your doctor will tell you if you should change the amount of sodium (salt) you ingest in your diet, your use of diuretics or other medications, or your exercise routine for aldosterone testing.

Aldosterone levels fall to very low levels with severe illness, so testing should not be done at times when a person is very ill. Stress and strenuous exercise can temporarily increase aldosterone results.