LabMed

Primary Aldosteronism (Conn's Syndrome)

At a Glance

Primary aldosteronism often presents as hypertension that is relatively resistant to antihypertensive medications. The cause of hypertension in most patients is unknown (essential hypertension); however, a need for further evaluation of hypertension and the possibility of primary aldosteronism is suggested by several factors:

  • moderate or extreme hypertension

  • diastolic hypertension

  • resistance to therapy

  • hypokalemia

  • observation of an adrenal mass (incidentaloma) on imaging studies

Cardiac palpitations may be another symptomatic presentation of primary aldosteronism. Patients with hypokalemia can present with muscle weakness or paralysis.

Primary aldosteronism is one of the most common identifiable causes of hypertension. Recent studies suggest that up to 10% of hypertensive patients may have primary aldosteronism. Earlier studies did not consider the diagnosis without hypokalemia and yielded lower estimates of less than 1% of hypertensive patients. Hypokalemia is no longer needed to make the diagnosis of primary aldosteronism.

Primary hyperaldosteronism results from secretion of aldosterone without the usual stimulus by the renin-angiotensin system. Nonregulated aldosterone production may result from a single adrenal adenoma, bilateral adrenal hyperplasia, a mineral corticoid producing adrenal carcinoma, or a rare inherited disorder, glucocorticoid suppressible aldosteronism. The term Conn’s syndrome was originally applied to adrenal adenomas producing aldosterone.

The primary effect of aldosterone is on distal renal tubules, sweat glands, and salivary glands. Aldosterone stimulates sodium-potassium exchange. In the kidney, aldosterone increases sodium uptake and potassium excretion. Retention of sodium results in slight volume expansion and increased blood pressure. Volume expansion tends to suppress renin and angiotensin production. Under normal physiology, aldosterone production would then fall. Other tissues, including the heart, have the mineralocorticoid receptors that bind aldosterone. Aldosterone, thus, may directly promote left ventricular hypertrophy and heart failure.

What Tests Should I Request to Confirm My Clinical Dx? In addition, what follow-up tests might be useful?

The primary screening test for primary aldosteronism is the plasma aldosterone:renin ratio. Aldosterone production is increased, and renin release is suppressed; therefore, the ratio is increased in primary aldosteronism. Renin can be determined either by a direct immunoassay of the renin molecule or by an activity assay measuring angiotensin production in the test tube. Serum potassium was once considered a key diagnostic factor.

Although hypokalemia supports the diagnosis, most patients with primary aldosteronism are now recognized as having potassium within reference limits.

Increased urine potassium concentration (>30 mmol/L) in a random urine specimen suggests increased mineralocorticoid effect.

Some tumors may produce increased amounts of other mineralocortoids in addition to aldosterone. 11-deoxycorticosterone and 18-hydroxycorticosterone, for example, have significant mineralocorticoid effect. Increases in serum 11-deoxycorticosterone or 18-hydroxycorticosterone suggest presence of an adrenal adenoma or adrenal carcinoma.(Table 1)

Table 1.

Test Results Indicative of the Disorder
Aldosterone:ReninRatio Serum Potassium Urine Potassium
Increased Low or normal Increased

Are There Any Factors That Might Affect the Lab Results? In particular, does your patient take any medications - OTC drugs or Herbals - that might affect the lab results?

Aldosterone production is stimulated by angiotensin generation by renin, high serum potassium concentration, and, to a lesser extent, adrenocorticotropin (ACTH).

Many factors affect the activity of the renin-angiotensin-aldosterone system (RAAS). These include posture, salt intake, and antihypertensive medicines. To assess the plasma aldosterone:renin ratio, patients should have a normal salt intake and should not take spironolactone, licorice, which is present in some candies, herbal preparations, or chewing tobacco.

Reference ranges are different for ambulatory (upright) patients than recumbent patients. Factors expanding vascular volume, such as increased salt intake, intravenous fluid infusion, mineralocorticoids, and recumbency suppress the RAAS. Factors contracting vascular volume, such as low salt intake, dehydration, diuretics, and upright posture, activate the RAAS.

Thiazide and loop diuretics promote potassium loss and need considered in assessing hypokalemia. Several antihypertensive agents, such as verapamil, hydralazine, prazosin, doxazosin, and terazosin, are considered to have minimal effects on aldosterone levels. The aldosterone:renin ratio is increased slightly by beta blockers, clonidine, nonsteroidal anti-inflammatory agents, renin inhibitors, and renal impairment, possibly leading to false-positive results for the screening test. The ratio is lowered by most diuretics, angiotensin converting enzyme inhibitors, angiotensin receptor blockers, some calcium channel blockers, sodium restriction, pregnancy, and renovascular hypertension.

Blood specimens for testing of plasma renin activity should be kept at room temperature; refrigeration of specimens may cause activation and higher values.

What Lab Results Are Confirmatory?

Confirmatory tests that can be applied when the plasma aldosterone:renin ratio is high include the oral sodium loading test, saline infusion test, fludrocortisones suppression test, and captopril challenge test. All of these challenge tests tend to physiologically suppress aldosterone, and failure to achieve suppression indicates loss of normal physiological regulation. Selection of which test to use depends on local practice and experience. Other tests may be employed to confirm the diagnosis and direct further therapy. Treatment with dexamethasone can assess whether aldosterone production is steroid responsive. A trial of spironolactone helps confirm that aldosterone is a cause of hypertension.

What Tests Should I Request to Confirm My Clinical Dx? In addition, what follow-up tests might be useful?

In assessing treatment options, it is important to distinguish between adrenal adenomas and hyperplasia. Imaging studies with computerized tomography (CT) can identify the presence of adrenal masses, but it does not indicate whether masses are functional. Adrenal venous sampling to collect specimens for measuring aldosterone and renin is a technically difficult procedure that helps assess whether aldosterone production is unilateral or bilateral.

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