What are the preparation requirements for a patient undergoing aldosterone (aldosterone) testing?

Aldosterone Testing Preparation

Patients undergoing aldosterone testing must be potassium-replete, have blood drawn in the morning after being out of bed for 2 hours and seated for 5-15 minutes, and ideally have interfering medications discontinued when clinically feasible—particularly mineralocorticoid receptor antagonists for at least 4 weeks, and ACE inhibitors/ARBs for at least 2 weeks. 1, 2

Potassium Repletion

• Ensure serum potassium is in the normal range (ideally 4.0-5.0 mEq/L) before testing, as hypokalemia suppresses aldosterone production and causes false-negative results. 1
• Provide potassium supplementation if needed to achieve adequate repletion prior to blood collection. 1
• This is critical because hypokalemia can directly suppress aldosterone secretion, undermining test accuracy. 1

Medication Management

Medications That MUST Be Withdrawn

• Mineralocorticoid receptor antagonists (spironolactone, eplerenone) must be withdrawn for at least 4 weeks before testing. 1, 2
• ACE inhibitors and ARBs should be discontinued for at least 2 weeks prior to testing, as they significantly increase renin levels and decrease aldosterone levels, causing false-negative results. 2
• Beta-blockers, centrally acting drugs (alpha-methyldopa), and diuretics should be stopped when clinically feasible, as these suppress renin and cause false-positive results. 1, 2, 3

Safe Alternative Medications During Testing

• Long-acting calcium channel blockers (verapamil slow-release) and alpha-receptor antagonists (prazosin, doxazosin) are preferred alternatives as they minimally interfere with the aldosterone-to-renin ratio. 1
• Hydralazine is also acceptable and causes minimal interference. 1, 4

When Medications Cannot Be Stopped

• If medications cannot be safely discontinued due to severe hypertension, interpret results in the context of the specific medications the patient is taking. 1
• Testing may be attempted during treatment with beta-blockers, ACE inhibitors, and ARBs, but results must be interpreted knowing these drugs' effects on renin and aldosterone. 4
• Beta-blockers suppress renin and increase the false-positive rate by artificially elevating the aldosterone-to-renin ratio. 3

Dietary Requirements

• Patients should maintain unrestricted (liberal) salt intake before and during testing. 1, 2
• Normal dietary sodium is essential because sodium restriction can physiologically increase aldosterone and confound interpretation. 1

Blood Collection Timing and Position

• Collect blood in the morning (ideally 0800-1000 hours) after the patient has been out of bed for at least 2 hours. 1
• The patient must be seated for 5-15 minutes immediately before blood draw. 1
• Blood should be drawn with the patient in a seated position, as posture affects renin and aldosterone levels. 1

Test Interpretation Thresholds

• A positive screening test requires BOTH an aldosterone-to-renin ratio (ARR) ≥20-30 ng/dL per ng/mL/hr AND a plasma aldosterone concentration ≥10-15 ng/dL. 1
• The specificity improves if a minimum plasma renin activity of 0.5 ng/mL/h is used in calculations. 1
• Note that cutoff values may differ when using liquid chromatography-tandem mass spectrometry (LC-MS/MS), which shows lower values than immunoassays. 5

Common Pitfalls to Avoid

• Do not rely on hypokalemia as a screening trigger, as it is absent in approximately 50% of primary aldosteronism cases. 1
• Monitor for rebound hypokalemia when mineralocorticoid receptor antagonists are withdrawn, especially in patients with confirmed primary aldosteronism. 2
• Avoid testing patients on spironolactone or eplerenone without the required 4-week washout period, as this makes confirmatory testing unreliable. 1
• Be aware that antihypertensive medications affect test accuracy differently—beta-blockers particularly increase false-positive rates by suppressing renin. 3

Next Steps After Positive Screening

• All positive ARR screening tests require confirmatory testing (intravenous saline suppression test or oral sodium loading with 24-hour urine aldosterone measurement) to demonstrate autonomous aldosterone secretion. 1
• Confirmatory testing should also be performed with unrestricted salt intake and normal serum potassium levels. 1
• Refer all patients with confirmed primary aldosteronism to a hypertension specialist or endocrinologist for subtype determination and treatment planning. 1