Validation of the Spot Urine in Evaluating 24-Hour Sodium Excretion in Chinese Hypertension Patients

Abstract

Background: The spot urine method as an alternative approach in estimating daily urine sodium excretion has been proposed for many years. Kawasaki has created an equation to predict daily urinary sodium excretion using second morning urine (SMU) samples which was obtained before breakfast after initial voiding upon arising. Tanaka has developed another equation by examining spot urine samples submitted at random times during the day. A newly published study proposed that the "PM sample," collected in the late afternoon or early evening before dinner, showed a stronger relationship with actual sodium excretion. We aimed to verify the effectiveness of these methods in evaluating 24-hour urinary sodium in Chinese hypertensive patients.

Methods: A total of 334 hypertensive participants were eligible to participate in this study. A total of 222 patients provided qualified SMU samples, Post Meridiem (PM) samples, and complete 24-hour urine collections.

Results: Biases using the Kawasaki formula were 2.1 mmol/day for the SMU specimens; for the Tanaka equation, biases of SMU and PM samples were 21.1 and 30.1 mmol/day, respectively. The highest intraclass correlation coefficient (ICC) was 0.64 when the Kawasaki formula was used in PM specimens, with the lowest ICC 0.17 when it is used in SMUs.

Conclusions: Spot urine method is acceptable for estimating 24-hour urinary sodium excretion in hypertensive individuals. Kawasaki's formula is useful for estimating population mean levels of sodium excretion from SMU, although it is not suitable for estimating individual sodium excretion.

Keywords: 24-hour collection; blood pressure; estimation; hypertension; spot urine; urinary sodium excretion; validation..