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 3 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 3 consecutive days from December 2023 to December 2024. Daily fasting blood and 24h urine samples were collected before, on the second day, and on the third day of the OSLT.

Results: 12 PA patients [median age of 51.5 (42.0∼57.0) years, 75% men] and 12 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 24h urinary sodium> 200 mmol/24h. 24h urinary aldosterone (UALD) 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/24h, P=0.583], as well as in healthy participants [2.65 (1.67∼3.82) vs. 2.63 (1.63∼4.34) μg/24h, P=0.747]. There was a strong correlation of 24h UALD 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.