Estimation of 24-hour urinary sodium, potassium, and creatinine excretion in patients with hypertension: can spot urine measurements replace 24-hour urine collection?

Abstract

Owing to inconvenience of a 24‑hour urine collection, diagnostic methods based on spot urine samples are becoming increasingly popular. Spot urine sodium measurements could replace 24‑hour urinary sodium (24hUNa) excretion, considered a surrogate measure of dietary sodium intake. Spot urine-based approaches to estimating 24hUNa and 24‑hour urinary potassium (24hUK) excretion are potentially useful in patients with hypertension, for example, to identify increased urinary potassium excretion in individuals with primary aldosteronism and high dietary sodium intake in those with resistant hypertension. In this review, we summarized our research on spot urine-based estimation of 24hUNa, 24hUK, and 24‑hour urinary creatinine (24hUCr) excretion to avoid the need for a 24‑hour urine collection in patients with hypertension. We found that the Pan American Health Organization (PAHO) formula was generally the best for predicting the average 24hUNa and 24hUK excretion in hospitalized patients with hypertension, while the Kawasaki equation was inferior for estimating 24hUNa and the Tanaka equation was inferior for estimating 24hUK excretion. However, all 3 equations were imprecise in terms of estimating individual 24hUNa or 24hUK excretion. We also confirmed the general utility of the equations for estimating 24hUCr excretion in hypertensive individuals but with significant differences between various equations, the best formulas being Chronic Kidney Disease Epidemiology Collaboration (CKDEPI) and Rule. Compared with the combined PAHO/CKD‑EPI formula, the Tanaka and Kawasaki equations underestimated increased 24hUNa and 24hUK excretion. Thus, the combined PAHO/CKD‑EPI formula might be the best for identifying increased 24hUNa and 24hUK excretion in patients with hypertension.