24-Hour Urine Aldosterone Collection: Storage Requirements
For a 24-hour urine aldosterone test, collect the urine in a plastic container and refrigerate it throughout the collection period—room temperature storage is NOT acceptable.
Storage Protocol
The urine specimen must be kept cold during the entire 24-hour collection period 1. Here's the proper approach:
- Use a plastic container (not glass)
- Refrigerate continuously at 4°C throughout the collection
- Keep the container in the refrigerator between voids
- Return it to refrigeration immediately after each void
Why Refrigeration Matters
Aldosterone degrades significantly at room temperature. Research demonstrates that urinary aldosterone shows poor stability without proper cold storage 1. When urine samples are kept at room temperature versus refrigerated conditions, aldosterone measurements show unacceptable variation (coefficient of variation ranging from 16-57% in the presence of various conditions) 1.
Critical Pitfall: Acid Preservatives
Do NOT add acid preservatives (like HCl) to the collection container for aldosterone measurement. This is a common error that will ruin your test. Studies show that aldosterone performs poorly in the presence of acid preservatives, with CVs up to 57% 1. Acid preservatives are needed for other analytes like cortisol, citric acid, and oxalate—but they interfere with aldosterone measurement.
Practical Collection Instructions
The 2025 Endocrine Society guideline specifies that for the oral sodium suppression test (which uses 24-hour urine aldosterone), you should 2:
- Collect the full 24-hour specimen on the final day of high sodium intake (4-5 g/day for 3-4 days)
- Measure urinary aldosterone, sodium, and creatinine from this collection
- Ensure adequate collection (24-hour urine sodium should ideally be >200 mEq/24 hours)
- Normalize serum potassium before testing, as hypokalemia causes false-negative results
Bottom Line
Cold storage is non-negotiable for accurate aldosterone measurement. Room temperature storage will lead to significant degradation and unreliable results that could miss the diagnosis of primary aldosteronism—a condition affecting up to 14% of hypertensive patients and associated with increased cardiovascular morbidity 3.