Development and Validation of a Prediction Model for Estimating 24-Hour Urinary Sodium Excretion Using Spot Urine Samples in Adult Patients

Abstract

Introduction

The measurement of urinary sodium excretion provides valuable information about an individual's sodium balance and can help in the management of various medical conditions. However, the collection of 24-hour urine samples is subject to errors. Spot urine sodium (uNa) measurements are a reliable alternative to 24-hour urine collections for estimating urinary sodium excretion.

Objective

To assess whether 24-h urinary sodium excretion (24 h uNa) can be estimated from spot samples in adult patients who attend hospital clinics.

Design and Methods

A cross-sectional study with a development (284 patients) and a validation cohort (229 patients) was conducted at our hospital. A multivariate linear regression model was built which was compared with former models. Concordance analyses and comparison of the ability to correctly classify each patient against a prespecified uNa cutoff value of 130 mmol/24 h were performed, assessed by the C-statistic.

Results

The model was well calibrated (slope [95% confidence interval] in internal validation: 0.965 [0.947-0.987], showing good discrimination, and performed robustly in an external validation cohort (slope: 0.811 [0.675-0.946]). The mean bias between the measured and the estimated 24 h uNa by NaRYC was 24.85 mmol/24 h [17.06-32.63]. The NaRYC had the highest values of Pearson coefficient (0.613 P < .0001), accuracy (the percentage of estimated 24 h uNa results within 30% deviation of measured 24 h uNa): 56.8%, and area under the receiver operating characteristic curve: 0.822 [0.766-0.869] as compared to other seven equations.

Conclusion

Although the mean bias of the results is quite acceptable, the variability observed in the 95% confidence interval makes not recommend the general use of a spot as a substitute of the 24-hour urine in order to estimate the total urine excretion of Na in a single subject basis.