From the Guidelines
Primary Hyperaldosteronism (Conn's Syndrome) Lab Findings
Primary hyperaldosteronism, also known as Conn's syndrome, is characterized by elevated plasma aldosterone levels and suppressed plasma renin activity. The typical lab findings include:
- Elevated plasma aldosterone levels, typically exceeding 15 ng/dL 1
- Suppressed plasma renin activity, often below 1.0 ng/mL/h 1
- Hypokalemia, with serum potassium levels less than 3.5 mmol/L, although this is not always present 1
- Metabolic alkalosis, with elevated serum bicarbonate levels above 28 mmol/L 1
Diagnostic Confirmation
The diagnosis of primary hyperaldosteronism can be confirmed by:
- Administering a saline infusion test, where 2 liters of 0.9% saline solution are infused over 4 hours, and plasma aldosterone levels remain elevated above 10 ng/dL at the end of the test 1
- Oral sodium loading test (with 24-h urine aldosterone) or IV saline infusion test with plasma aldosterone at 4 h of infusion 1
- Adrenal vein sampling to determine whether the increased aldosterone production is unilateral or bilateral in origin 1
Key Points
- The aldosterone-to-renin ratio is a useful screening test for primary hyperaldosteronism, with a ratio greater than 30 suggesting the diagnosis 1
- Patients with primary hyperaldosteronism may exhibit resistant hypertension, hypokalemia, and metabolic alkalosis 1
- The condition can be caused by unilateral adrenal adenoma or bilateral adrenal hyperplasia 1
From the Research
Lab Findings for Primary Hyperaldosteronism (Conn's Syndrome)
The lab findings for primary hyperaldosteronism (Conn's syndrome) include:
- High plasma and urinary aldosterone levels 2
- Suppressed plasma renin activity (PRA) 2, 3
- Elevated aldosterone/renin ratio 2, 3, 4
- Normal to high normal PRA levels in some cases, despite high aldosterone levels 2
- High serum creatinine levels and hyperkalemia after spironolactone treatment 2
- Failure to suppress plasma aldosterone concentration (PAC) after saline infusion 5, 4
Diagnostic Criteria
The diagnostic criteria for primary hyperaldosteronism include:
- Elevated aldosterone/renin ratio 3, 4
- Failure to suppress PAC after saline infusion 5, 4
- PAC above 10 ng/dL (>277 pmol/L) after saline infusion 6
- PAC above 14 ng/dL (397 pmol/L) at 120 minutes after saline infusion 5
Prevalence and Presentation
Primary hyperaldosteronism can occur in approximately 5-15% of hypertensive patients, with many cases presenting with normal serum potassium concentrations 3, 6
- The prevalence of primary hyperaldosteronism may vary among different populations, with a study in Singapore finding a prevalence of at least 5% in the adult Asian hypertensive population 6
- Hypokalemia is not a reliable predictor of primary hyperaldosteronism, as many patients may have normal serum potassium levels 2, 3, 6