What are the lab findings in Conn's (Primary Aldosteronism) syndrome?

From the Guidelines

In patients with Conn's syndrome, also known as primary aldosteronism, lab findings typically include elevated serum aldosterone levels, often exceeding 20 ng/dL, and suppressed plasma renin activity, usually below 1.0 ng/mL/h [ 1 ].

Key Lab Findings

• Hypokalemia, with serum potassium levels often below 3.5 mmol/L
• Metabolic alkalosis, with elevated serum bicarbonate levels
• Elevated aldosterone-to-renin ratio (ARR), typically above 30, which can be used as a screening test for the condition [ 1 ]

Important Considerations

• The ARR result needs to be interpreted in the context of the specific medication(s) the patient is taking [ 1 ]
• Hypokalemia is absent in the majority of cases and has a low negative predictive value for the diagnosis of primary aldosteronism [ 1 ]
• The diagnosis of primary aldosteronism generally requires a confirmatory test, such as the intravenous saline suppression test or oral salt-loading test [ 1 ]

From the Research

Lab Findings in Conn's Syndrome

The lab findings in Conn's syndrome, also known as primary aldosteronism, include:

• Elevated aldosterone levels 2, 3, 4, 5, 6
• Low plasma renin activity (PRA) 3, 4, 5, 6
• High aldosterone to renin ratio (ARR) 2, 3, 4
• Hypokalemia (low serum potassium levels) 2, 3, 4, 5, 6
• Hypernatremia (high serum sodium levels) 6
• Elevated creatinine phosphokinase (CPK) levels in cases of rhabdomyolysis 5

Diagnostic Tests

The following diagnostic tests are used to confirm primary aldosteronism:

• Measurement of the aldosterone-renin ratio (ARR) as a first screening test 2, 3, 4
• Aldosterone suppression testing to confirm inappropriate aldosterone secretion 4
• Imaging of the adrenal glands to differentiate between unilateral and bilateral adrenal disease 2
• Selective adrenal vein catheterization as the current gold standard for diagnosis 2
• Functional imaging techniques and measurement of steroid profiles as promising alternatives to adrenal vein catheterization 2

Subtype Evaluation

The following tests are used to evaluate the subtype of primary aldosteronism:

• Imaging of the adrenal glands to identify adrenal tumors or hyperplasia 2, 5, 6
• CT scan to evaluate the adrenal glands 5, 6
• Saline suppression test to confirm aldosterone secretion and renin activity 6