Conn's Syndrome

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The goal when looking for Conn’s syndrome is for tests to understand where the aldosterone is coming from. The conclusions made from these tests may then help decide whether surgery is likely to be beneficial or the condition can be treated with drugs.

Laboratory Tests
Electrolytes, usually blood sodium, potassium and sometime chloride and bicarbonate may be measured to look for an electrolyte imbalance. If an imbalance is seen, then the doctor may give the patient spironolactone, a drug that blocks the action of aldosterone, to see if balance is restored. Hypertension is treated according to NICE guidelines with diuretic drugs, beta-blockers, inhibitors of angiotensin converting enzyme (ACE), calcium channel blockers alone or in combinations according to ethnicity, gender and age. Doctors will frequently request blood renin tests along with aldosterone tests in blood samples or in a 24-hour urine collection to help diagnose primary hyperaldosteronism and to monitor the effectiveness of treatment. The ratio of aldosterone to renin is used as an early test for primary hyperaldosteronism. If aldosterone is high and renin levels are low, then the ratio will be significantly increased and primary hyperaldosteronism is likely to be present.

If hyperplasia or an aldosterone-producing tumour is suspected, but not seen using normal procedures, then a doctor may request confirmatory tests during a hospital admission. Oral sodium loading or saline infusion should be used with caution in patients with uncontrolled hypertension. Fludrocortisone suppression or a captopril challenge tests are used in specialist centres. It will be necessary for drug treatment to be discontinued. Primary hyperaldosteronism is indicated by an elevated aldosterone/renin ratio at 08.00h. A low renin activity that shows little or no increase after 30 min of mobility also supports autonomous aldosterone secretion. To aid the distinction between hyperaldosteronism due to adrenal adenoma and that due to bilateral adrenal hyperplasia, it may be helpful to consider the plasma aldosterone concentrations at 08.00h and 12.00h. In normal subjects and patients with adrenal hyperplasia the aldosterone rises on standing. If cortisol values between 08.00h and 12.00h show a decrease due to normal diurnal rhythm, an elevated aldosterone level at 08.00h decreasing by 50% or more at 12.00h is suggestive of an adenoma or GRA.

Adrenal venous sampling is a definitive confirmatory test. In this procedure, blood is collected from the vein that carries blood away from each adrenal gland. A catheter will be inserted into a vein in the thigh and moved up inside a large vein in the back to the the adrenal veins. The correct location is seen by imaging. The adrenal vein blood samples from each side 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 present in the gland with the highest aldosterone concentration.

Non-Laboratory Tests

  • Blood pressure measurement - often the first indicator of possible primary hyperaldosteronism
  • CT (computed tomography) scan or MRI (magnetic resonance imaging) are used to locate adrenal tumours. Determining large adrenal glands (hyperplasia) can be tricky because the size of normal adrenal glands varies a lot from one person to the next.. The interpretation of the scan can also be complicated as benign adrenal tumours are relatively common, especially as people become older. Many of these benign tumours do not produce aldosterone or other hormones and are found during investigations for other reasons.

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