LAUSR

Objectives: Spot urine is increasingly used to estimate 24-hour urinary sodium excretion (24-h USE). Kawasaki, INTERSALT, Tanaka, Sun-SMU and Sun-PM equations are used to predict 24-h USE using second morning urine (SMU), random spot urine and post meridiem (PM) samples respectively. We aimed to assess the validity of existing equations in estimation of 24-h USE in Chinese population. Methods: From October 2015 to January 2016, a convenience sample of 100 healthy volunteers (42% males) aged from 21 to 79 years provided each spot urine sample within 24 hours. SMU and PM samples were selected according to voiding time. 24-hour urinary samples were obtained by mixing each spot urine sample. The existing equations were used to estimate 24-h USE with suitable spot urine samples. We compared measured vs. estimated measurements by correlation coefficient, bias (measured minus estimated 24-h USE) and Bland-Altman plots. Results: The average of 24-h USE was 4377.00 ± 2311.95 mg/d. The estimated values of the existing equations ranged from 3171.95 mg/d (INTERSALT) to 5406.32 mg/d (Kawasaki). The highest correlation coefficient was 0.485 from Tanaka equation. The least bias was − 6.47 mg/d (95% confidence interval (95% CI): − 419.80, 406.87 mg/d) from Tanaka equation while the highest was 1205.05 mg/d (95% CI: 745.97, 1664.12 mg/d) from INTERSALT equation. The Bland-Altman plots indicated that the differences between the measured and estimated measurements appeared to increase as the means of 24-h USE increased. Conclusion: We found a poor agreement between estimated and measured 24-h USE among Chinese population. Although Tanaka equation produced the least bias overall, no single equations worked well. New equations are needed to accurately estimate 24-h USE in Chinese population.