Association between urinary salt excretion and albuminuria in Japanese patients with chronic kidney disease: the Fukuoka kidney disease registry study

Background: Several large population-based studies have demonstrated that urinary salt excretion (USALT) is associated with albuminuria. However, this relationship has not been assessed in a large cohort study of patients with chronic kidney disease (CKD). Thus, the present study aimed to elucidate whether USALT was independently associated with albuminuria in a large cohort of patients with CKD. Methods: This cross-sectional study was conducted in 4075 patients with CKD not on dialysis. USALT (g/day) was estimated from spot urine. Patients were divided into quartiles (Q1–Q4) according to estimated USALT. Multivariable regression models were used to determine whether USALT was independently related to urinary albumin-to-creatinine ratio (UACR) or the presence of macroalbuminuria. Results: In multivariable linear regression analyses, 1-g/day increment in USALT was significantly associated with log UACR [coefficient 0.098, 95% confidence interval (CI) 0.075–0.121]. In addition, compared with the first USALT quartile, the third and fourth quartiles exhibited significant associations with log UACR (Q3: coefficient 0.305, 95% CI 0.154–0.456; Q4: coefficient 0.601, 95% CI 0.447–0.756). Furthermore, multivariable logistic regression analyses showed that USALT (1-g/day increment) was significantly associated with the presence of macroalbuminuria [odds ratio (OR) 1.11, 95% CI 1.07–1.14]; the third and fourth USALT quartiles exhibited significantly greater risks of macroalbuminuria, compared with the first quartile (Q3: OR 1.33, 95% CI 1.09–1.62; Q4: OR 1.89, 95% CI 1.54–2.32). Conclusions: This significant association of USALT with UACR and macroalbuminuria suggests that higher USALT may cause increased albuminuria, thereby contributing to kidney disease progression.