Simplification of the Oral Sodium Loading Test: 2-Day Method Replacing 3-Day Method.

OBJECTIVES

As one of the diagnostic tests for primary aldosteronism (PA), the oral sodium loading test (OSLT) usually takes three days, which is time-consuming. This study aims to investigate the possibility of the 2-day method replacing the 3-day method in the OSLT.

METHODS

In this prospective study, both PA patients and healthy participants were recruited and underwent an oral high-sodium diet for three consecutive days from December 2023 to December 2024. Daily fasting blood and 24-hour urine samples were collected before, on the second day, and on the third day of the OSLT.

RESULTS

Twelve PA patients [median age of 51.5 (42.0∼57.0) years, 75% men] and twelve healthy participants [median age of 30.5(24.0-39.8) years, 25% men] were recruited in this study. After oral sodium loading, all participants had a 24-hour urinary sodium> 200 mmol/24 h. Twenty-four hour urinary aldosterone was not significantly different between the second day and the third day in PA patients [18.24 (15.58∼33.83) vs 17.25 (12.74∼27.06) μg/24 h, P = .583], as well as in healthy participants [2.65 (1.67∼3.82) vs 2.63 (1.63∼4.34) μg/24 h, P = .747]. There was a strong correlation of 24-hour urinary aldosterone on the second day and the third day in both PA patients and healthy participants (r = 0.8322 and 0.9333, respectively). Aldosterone-related steroid hormone profile showed no statistically significant difference between the two days, either for PA patients or for healthy participants.

CONCLUSIONS

This study confirms that the 2-day method can replace the 3-day method in OSLT for a more convenient diagnosis of PA.