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Conn Syndrome

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Tests

The goals of testing for Conn syndrome are to identify primary aldosteronism, distinguish between primary and secondary aldosteronism, and distinguish between those causes of Conn syndrome that may benefit from surgical intervention and those that will usually not.

Laboratory Tests

  • Electrolytes may be measured to look for an electrolyte imbalance, primarily decreased potassium and chloride along with increased carbon dioxide.
  • Doctors will frequently order blood renin tests along with blood and/or 24-hour urine aldosterone tests to help diagnose primary aldosteronism and to monitor the effectiveness of treatment. The ratio of aldosterone to renin (ARR) is used to test for primary aldosteronism. If renin levels are low and aldosterone levels are high, then the ratio will be significantly increased and primary aldosteronism is the likely diagnosis. Based on the results of these tests, a doctor may do a suppression test, using sodium chloride or captopril administration, to see if aldosterone secretion decreases.

These tests may be followed by a CT (computed tomography) or MRI (magnetic resonance imaging) scan of the adrenal glands to look for a tumor. This process can be complicated as benign adrenal tumors are relatively common, especially as people get older. Many of them do not secrete aldosterone and are found incidentally during procedures performed 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 tumor 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 is calculated) and then the results from the two adrenal glands are compared. If they are significantly different, then it is likely that an adenoma is located in the gland with the highest aldosterone concentration.

Non-Laboratory Tests

  • Blood pressure measurement – often the first indicator of possible primary aldosteronism
  • CT (computed tomography) scan or MRI (magnetic resonance imaging) – used to detect adrenal tumors

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