Association between the urinary sodium-to-potassium ratio and apparent treatment-resistant hypertension in Japanese patients with non-dialysis dependent chronic kidney disease: the Fukuoka Kidney disease Registry study.

Recently, an association between the urinary sodium-to-potassium (U-Na/K) ratio and apparent treatment-resistant hypertension (aTRH) has been found in Western patients with chronic kidney disease (CKD). However, little information is available from Asian CKD cohorts, who typically consume a higher Na and lower K diet than Western populations. We analysed 4102 patients with CKD from the Fukuoka Kidney disease Registry study, which was a multicentre cohort study. The main exposures were the U-Na/K ratio, estimated urinary Na excretion (eUNa) and urinary K excretion (eUK). The primary outcome was aTRH, which was defined as inadequate blood pressure control treated with three antihypertensive medication classes or treatment with four or more classes regardless of blood pressure. Additionally, we evaluated the predictive performance of the U-Na/K ratio using net reclassification improvement. Among the patients, 701 (17.0%) had aTRH. The multivariable-adjusted odds ratio (95% confidence interval) for aTRH was significantly higher in the highest U-Na/K ratio group (Q4) than in the lowest U-Na/K ratio group (Q1) (1.36 [1.05-1.75], p = 0.02, p for trend = 0.01), but the association between eUNa or eUK and aTRH was not significant. Furthermore, when the U-Na/K ratio was incorporated into a model with conventional atherosclerotic factors, the net reclassification improvement was 0.09 (p = 0.03). This study shows a significant association between the U-Na/K ratio and aTRH in Asian CKD. Moreover, the U-Na/K ratio can provide additional predictive value for identifying patients at risk of aTRH beyond conventional risk factors.