Urinary sodium-to-potassium ratio and blood pressure in chronic kidney disease

Abstract Introduction In the general population, urinary sodium-to-potassium (uNa/K) ratio associates more strongly with high blood pressure (BP) than either urinary sodium or potassium alone. Whether this is also the case among patients with chronic kidney disease (CKD) is unknown. Methods We studied the associations of spot urine sodium-to-creatinine (uNa/Cr), potassium-to-creatinine (uK/Cr), and uNa/K ratios with a single office BP reading in 1660 patients with moderate to severe CKD at inclusion in the CKD-REIN cohort. Results Patients' median age was 68 (IQR 59-76) years; most were men (65%), had moderate CKD (57%), and albuminuria (72%). Mean systolic and diastolic BP was 142/78 mm Hg. Spot uNa/Cr and uNa/K ratios were positively associated with systolic, mean arterial, and pulse pressures. The mean adjusted difference in systolic BP between the highest and the lowest quartile (Q4 vs Q1) was 4.24 (95% CI, 1.53-6.96) mm Hg for uNa/Cr and 4.79 (95% CI, 2.18-7.39) mm Hg for uNa/K. Quartiles of spot uK/Cr were not associated with any BP index. The higher the quartile of uNa/K, the higher the prevalence ratio of uncontrolled (Q4 vs Q1 1.43, 95% CI 1.19-1.72) or apparently treatment-resistant hypertension (Q4 vs Q1 1.35, 95% CI 1.14-1.60). Findings were consistent in a subset of 803 individuals with two BP readings. Conclusion In patients with CKD, higher urinary sodium excretion is associated with higher BP, but unlike in general population, lower potassium excretion is not. Urinary Na/K does not add significant value in assessing high BP risk, except perhaps for hypertension control assessment.