Aldosterone-Renin Ratio Testing Requirements
Yes, the aldosterone-renin ratio (ARR) blood test should be performed in the morning after the patient has been out of bed for at least 2 hours and seated for 5-15 minutes immediately before blood collection. 1, 2
Timing Requirements
The test has specific timing requirements that are critical for accurate results:
- Blood must be drawn in the morning after the patient has been upright (out of bed) for 2 hours prior to collection 1, 2
- Patient should be seated for 5-15 minutes immediately before the blood draw 1, 2
- This standardized positioning and timing improves test sensitivity 3
Fasting Status
Fasting is NOT explicitly required for the ARR test. 1, 2 The guidelines emphasize timing, positioning, and medication management but do not mandate fasting. However, the test should be performed under highly standardized conditions to minimize variability. 4
Critical Pre-Test Preparation
Potassium Correction
- Patients must be potassium-replete before testing because hypokalemia suppresses aldosterone production and causes false-negative results 1, 2, 3
- Target serum potassium in the 4.0-5.0 mEq/L range 2
- This is a common pitfall: hypokalemia is absent in approximately 50% of primary aldosteronism cases, but when present, it must be corrected before testing 2
Dietary Sodium
- Encourage unrestricted (liberal) salt intake before testing 1, 2, 3
- Dietary salt restriction can stimulate renin and produce false-negative results 3
Medication Management
When clinically feasible, interfering medications should be adjusted:
Medications to STOP (cause false results):
- Beta-blockers, centrally acting drugs, and diuretics should be discontinued when possible 1, 2
- Mineralocorticoid receptor antagonists (spironolactone, eplerenone) must be withdrawn at least 4 weeks before testing 1, 2
- Beta-blockers and NSAIDs suppress renin, raising the ARR and causing false positives 3
- Diuretics, ACE inhibitors, and ARBs stimulate renin, lowering the ARR and causing false negatives 3
Safe alternatives to use:
- Long-acting calcium channel blockers (like verapamil slow-release) and alpha-receptor antagonists (prazosin, doxazosin, hydralazine) minimally interfere with ARR 1, 2, 3
Important caveat: If medications cannot be stopped safely, test the patient on their current medications and interpret results in the context of the specific drugs they are taking 1, 2. This is preferable to delaying diagnosis in patients with severe hypertension. 5
Test Interpretation Thresholds
A positive screening test requires BOTH criteria:
- ARR ≥20-30 ng/dL per ng/mL/hr (cutoff varies by guideline, with ≥20 having >90% sensitivity and specificity) 1, 2
- Plasma aldosterone concentration ≥10-15 ng/dL 1, 2
- Specificity improves if minimum plasma renin activity of 0.5 ng/mL/h is used 1, 2
Critical Pitfalls to Avoid
- Do not rely on a single ARR measurement - the test shows marked variability even when measured on the same day, particularly at higher ARR values 4
- Do not use hypokalemia as a screening trigger - it is absent in 50% of primary aldosteronism cases 1, 2
- Do not skip confirmatory testing - a positive ARR is only a screening test and requires confirmation with saline suppression or oral salt loading 1, 2
- Be aware that females have higher ratios than males, and false positives can occur during the luteal menstrual phase or with certain oral contraceptives 3
Next Steps After Positive Screening
All patients with positive ARR screening require:
- Confirmatory testing (intravenous saline suppression test or oral sodium loading with 24-hour urine aldosterone) to demonstrate autonomous aldosterone secretion 1, 2
- Referral to a hypertension specialist or endocrinologist for subtype determination and treatment planning 1, 2
- Adrenal venous sampling before considering surgery to distinguish unilateral from bilateral disease, as up to 25% of patients might undergo unnecessary adrenalectomy based on CT findings alone 2