APPLYING SPOT URINE SODIUM TO POTASSIUM RATIO IN A STANDARDIZED SPOT URINE COLLECTION TO IMPROVE THE ACCURACY OF 24-HOUR URINE SODIUM EXCRETION ESTIMATION

Introduction:

High sodium intake has been a well-established risk factor for various chronic diseases including incident chronic kidney disease (CKD) and accelerated CKD progression. Limiting dietary sodium intake to less than 2,000 mg is recommended. Apart from the dietary recall, collecting 24-hour urinary sodium excretion (USE) could evaluate sodium intake in the preceding day. However, the collection is not convenient in clinical practice. Many formulae have been developed from spot urine collection to estimate USE, but the performances are relatively unsatisfactory. Despite the established role of hypertension management with urinary sodium to potassium ratio (UNKR), none of the previous formulae adds spot urinary sodium to potassium ratio (UNKR) in the USE estimating equation, with some of them using a non-standardized spot urine collection.

Methods:

Stable patients visiting hypertension clinic in a teaching hospital who were willing to give an informed consent were included. Standardized 24-hour urine and second morning spot urine were collected for each patient. Spot urinary sodium (UNa), creatinine (UCr), potassium, UNKR, and anthropometric data were used to generate USE estimating formula with the highest coefficient of determination via backward and manual selection in linear regression analysis. The proposed formula was also compared with the existing formulae (Tanaka, Kawasaki, and INTERSALT) in predicting USE.

Results:

Fifty-five subjects (47% male, age 64±11 years, estimated glomerular filtration rate 64±11 mL/min/1.73 m2, USE 3013±1612 mg) were included. The chosen formula was USE = 11.266(UNKR) + 0.187(UCr in mg/dL) + (18.817 if male) + 3.628(height in cm) - 508.079. The formula resulted in a Pearson correlation coefficient of 0.641 which is higher than that of precious formulae (Figure 1). Using UNa without UKNR or UNa to UCr ratio in the regression analysis resulted in poorer estimating models.

Conclusions:

USE estimating equation using our proposed formulae with standardized second morning spot urine collection could improve care of hypertensive patients with a more convenient urine collection. External validation and expanded application of this formula in patients with CKD necessitate further studies.

I have no potential conflict of interest to disclose.

I did not use generative AI and AI-assisted technologies in the writing process.