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Urinary Sodium-to-Potassium Ratio and Blood Pressure in CKD
Natalia Alencar de Pinho1, Jean Kaboré2, Maurice Laville3
1University Paris-Saclay, UVSQ, University Paris-Sud, Inserm, Clinical Epidemiology team, CESP, Villejuif, France.
Insights
In chronic kidney disease (CKD) patients, higher urinary sodium excretion links to increased blood pressure (BP). The urinary sodium-to-potassium ratio offers limited value for assessing high BP risk, but may aid hypertension control assessment.
Area of Science:
- Nephrology
- Cardiovascular Medicine
- Clinical Chemistry
Background:
- The urinary sodium-to-potassium (uNa/K) ratio is a strong predictor of high blood pressure (BP) in the general population.
- It remains unclear if this association holds true for individuals with chronic kidney disease (CKD).
Purpose of the Study:
- To investigate the association between urinary sodium-to-creatinine (uNa/Cr), potassium-to-creatinine (uK/Cr), and uNa/K ratios with BP in patients with moderate to severe CKD.
- To determine if the uNa/K ratio provides additional value in assessing high BP risk or hypertension control in CKD patients.
Main Methods:
- Analysis of spot urine samples from 1660 patients with moderate to severe CKD.
- Assessment of associations between urinary ratios (uNa/Cr, uK/Cr, uNa/K) and office BP readings (systolic, diastolic, mean arterial, pulse pressures).
- Evaluation of the prevalence of uncontrolled or treatment-resistant hypertension across quartiles of urinary ratios.
Main Results:
- Higher spot uNa/Cr and uNa/K ratios were significantly associated with increased systolic, mean arterial, and pulse pressures.
- A 4.79 mm Hg increase in systolic BP was observed between the highest and lowest quartiles of uNa/K.
- Urinary potassium-to-creatinine (uK/Cr) ratios showed no association with any BP index. Higher uNa/K ratios correlated with increased prevalence of uncontrolled and treatment-resistant hypertension.
Conclusions:
- In CKD patients, elevated urinary sodium excretion is linked to higher BP.
- Unlike in the general population, lower urinary potassium excretion is not associated with higher BP in CKD patients.
- The urinary Na/K ratio offers minimal added value for high BP risk assessment in CKD, but may assist in evaluating hypertension control.
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.
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