Urinary Sodium-to-Potassium Ratio and Blood Pressure in CKD

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 (interquartile range [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% confidence interval [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 2 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.

Keywords: blood pressure; chronic kidney disease; potassium; salt; sodium.

Graphical abstract

Figure 1

Distribution of spot urine sodium-to-creatinine, potassium-to-creatinine, and sodium-to-potassium ratios according to (a) age, (b) gender, (c) estimated glomerular filtration rate (eGFR), (d) education level, and (e) body mass index (BMI). The boxes represent spot urine ratio median values and interquartile ranges (25th and 75th quartile); the whiskers, the minimum and maximum values after excluding outliers. uNa/Cr, urine sodium-to-creatinine ratio; uK/Cr, urine potassium-to-creatinine ratio; uNa/K, urine sodium-to-potassium ratio; eGFR, estimated glomerular filtration rate.

Figure 2

Crude and adjusted^a variations in systolic and diastolic blood pressure (BP), mean arterial pressure, and pulse pressure by quartiles of spot urine (a) sodium-to-creatinine, (b) potassium-to-creatinine, and (c) sodium-to-potassium ratios. The points and whiskers represent the mean estimate and 95% confidence intervals, respectively. ^aModel adjusted for age, gender, education level, estimated glomerular filtration rate, albuminuria category, history of diabetes, heart failure, dyslipidemia, body mass index, and number of antihypertensive drug classes. uNa/Cr, urine sodium-to-creatinine ratio; uK/Cr, urine potassium-to-creatinine ratio; uNa/K, urine sodium-to-potassium ratio.

Figure 3

Crude and adjusted^a prevalence ratios of hypertension (HT) status by quartiles of spot urine (a) sodium-to-creatinine, (b) potassium-to-creatinine, and (c) sodium-to-potassium ratios. The points and whiskers represent the mean estimate, and 95% confidence intervals, respectively. ^aModel adjusted for age, gender, education level, estimated glomerular filtration rate, albuminuria category, history of diabetes, heart failure, dyslipidemia, and body mass index. uNa/Cr, urine sodium-to-creatinine ratio; uK/Cr, urine potassium-to-creatinine ratio; uNa/K, urine sodium-to-potassium ratio.