What lab values are monitored in patients with hyperaldosteronism?

Laboratory Values Monitored in Hyperaldosteronism

Monitor the aldosterone-to-renin ratio (ARR), plasma aldosterone concentration, plasma renin activity, serum potassium, and serum sodium as the core laboratory parameters in patients with hyperaldosteronism. 1

Primary Screening Parameters

Aldosterone-to-Renin Ratio (ARR)

• The ARR is the single most important screening test, with a positive result defined as ARR ≥30 (when aldosterone is measured in ng/dL and renin activity in ng/mL/h). 1
• For a valid positive screen, plasma aldosterone concentration must be at least 10-15 ng/dL in addition to the elevated ratio. 1
• The specificity improves if a minimum plasma renin activity of 0.5 ng/mL/h is used in calculations. 1
• An ARR of 20 ng/dL per ng/mL/hr has excellent sensitivity and specificity (>90%) for confirming hyperaldosteronism. 1

Plasma Aldosterone Concentration

• Elevated plasma aldosterone (≥10-15 ng/dL) is required alongside an elevated ARR to interpret the screening test as positive. 1
• During confirmatory testing with intravenous saline suppression, failure to suppress plasma aldosterone below 5 ng/dL after 2L of normal saline over 4 hours confirms autonomous aldosterone secretion. 1

Plasma Renin Activity (PRA)

• Suppressed PRA is characteristic of primary aldosteronism due to aldosterone-induced sodium retention and mild extracellular volume expansion. 1
• Important caveat: In patients with severe hypertension and secondary kidney damage, PRA can escape suppression despite true primary aldosteronism, though the ARR remains elevated due to disproportionately high aldosterone levels. 2

Electrolyte Monitoring

Serum Potassium

• Hypokalemia is present in only approximately 50% of patients with primary aldosteronism—normal potassium does not exclude the diagnosis. 1
• Patients must be potassium-replete before testing, as hypokalemia can suppress aldosterone production and lead to false-negative results. 1
• Monitor for hyperkalemia when initiating mineralocorticoid receptor antagonist therapy, particularly in patients with renal impairment. 1

Serum Sodium

• Mild hypernatremia may occur due to aldosterone's action on the distal convoluted tubule causing sodium retention. 1
• Patients should have unrestricted salt intake before testing to ensure accurate interpretation. 1

Additional Laboratory Parameters

Serum Creatinine

• May be elevated, particularly in patients with severe hypertension and secondary kidney damage. 1
• Monitor closely when starting mineralocorticoid receptor antagonists, as serum creatinine may increase significantly due to decreased filtered sodium load and reduced mineralocorticoid function. 1, 2

24-Hour Urine Aldosterone

• Used as part of confirmatory testing with oral salt loading—elevated urinary aldosterone despite high sodium intake confirms autonomous secretion. 1
• Testing should be performed with unrestricted salt intake and normal serum potassium levels. 1

Critical Testing Conditions

Patient Preparation

• Collect blood in the morning, with the patient out of bed for 2 hours prior and seated for 5-15 minutes immediately before collection. 1
• Blood must be drawn with the patient in a seated position. 1

Medication Considerations

• Beta-blockers, centrally acting drugs, and diuretics should be stopped when feasible, as they suppress renin and cause false-positive ARR results. 1, 3
• Mineralocorticoid receptor antagonists must be withdrawn at least 4 weeks before testing. 1, 3
• Long-acting calcium channel blockers and alpha-receptor antagonists minimally interfere with ARR and can be used as alternatives. 1
• If medications cannot be stopped, interpret results in the context of the specific medications the patient is taking. 1

Common Diagnostic Pitfalls

• Do not rely on hypokalemia as a screening trigger—it is absent in 50% of primary aldosteronism cases. 1
• Low renin can artificially elevate the ARR even without truly elevated aldosterone levels, necessitating confirmatory testing. 4
• In patients with advanced kidney disease from severe hypertension, renin may not be fully suppressed despite true primary aldosteronism. 2
• Beta-blockers significantly interfere with screening by suppressing renin, increasing false-positive rates. 5