PS-P13-11: ASSOCIATION BETWEEN SPOT URINE SODIUM-TO-POTASSIUM RATIO AND BLOOD PRESSURE IN HEALTHY ADOLESCENTS: THE WAKAYAMA STUDY

Abstract

Objective: Spot urine sodium to potassium ratio (Na/K) is a simple measure of sodium loading and has been shown to be associated with blood pressure (BP) levels. This study aimed to evaluate the association between spot urine Na/K and BP in a cross sectional sample of healthy adolescent population. Design and method: The study participants consisted of 457 healthy adolescents (217 males and 240 females) aged 12 to 15 years (mean age: 13.9 years). Brachial arterial BP was measured in the supine position using digital BP monitor with an appropriate cuff size. Urinary Na, K, and creatinine levels were measured using spot urine specimens collected in the early morning of the sampling day. Results: The spot urine Na/K levels of participants was 4.99 ± 2.76 (Na, 148.1 ± 58.4 mEq/L; K, 36.1 ± 18.7 mEq/L), and there was no significant difference between males and females. When the participants were stratified based on the quartiles of urinary Na/K distribution (< 2.95, 2.95 to 4.54, 4.55 to 6.59, > = 6.6), systolic and diastolic BP gradually increased with an increase in Na/K levels (systolic BP, 106.1, 106.9, 108.2, and 111.5 mmHg, P for trend < 0.001; diastolic BP, 62.0, 62.4, 63.1, 64.3 mmHg, P for trend = 0.022). The Na/K was more closely associated with BP than urinary Na and K levels, as well as daily salt intake estimated from urinary Na. In multiple regression analysis, Na/K was significantly associated with systolic BP (β; = 0.144, P < 0.001) and diastolic BP (β; = 0.114, P = 0.015), independent of potential confounding factors. The BP of the subgroup with high Na/K (> = 6.6) and high salt intake (> = 8.5 g/day) was significantly higher than that of those with only high salt intake (systolic BP, 115.0 mmHg vs. 109.1 mmHg, P < 0.001; diastolic BP, 66.0 mmHg vs. 62.5 mmHg, P = 0.017). Conclusions: High Na/K levels is associated with elevated BP in healthy adolescents, and Na/K may be useful in assessing the effect of salt loading on BP than Na excretion alone.