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.
Doctors will frequently order blood renin tests along with blood and/or 24-hour urine aldosterone tests to help diagnose primary hyperaldosteronism and to monitor the effectiveness of treatment. 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. 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.
Electrolytes may be measured to look for an electrolyte imbalance – primarily decreased potassium and chloride but also increased bicarbonate. If they are present, then the doctor may give the patient spironolactone, a drug that blocks the action of aldosterone, to see if balance is restored.
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.