URINARY SODIUM TO POTASSIUM RATIO AS AN INDEX OF CARDIOVASCULAR HEALTH IN PATIENTS WITH RHEUMATOID ARTHITIS

Objective: Patients with autoimmune inflammatory diseases are at increased risk of cardiovascular complications. Rather than either sodium (Na) or potassium (K) intake alone, the ratio of Na-to-K has been introduced as a simple and useful indicator of diet quality and a more reliable index of cardiovascular risk assessment. The present study aimed to determine the clinical impact of Na-to-K ratio as a marker of cardiovascular health in patients with rheumatoid arthritis (RA). Design and method: We used the gold-standard method of measurement of Na and K in 24 h urine, to estimate urinary Na-to-K ratio in consecutive patients with RA. We further non-invasively assessed myocardial perfusion by measurement of subendocardial viability ratio (SEVR), also known as Buckberg index. Arterial stiffness was evaluated by measurement of pulse-wave velocity (PWV) and augmentation index normalized to 75 bpm (AIx@75), using applanation tonometry. Results: A total of 61 patients with RA were included aged 62.4±9.9 years, of whom the majority (78.7%) were females. Only two patients presented an optimal Na-to-K ratio of less than or equal to 1. A significant inverse relationship of urinary Na-to-K ratio was observed with HDL-C (r=-0.316, p=0.014) and renal function, as represented by estimated glomerular filtration rate (r=-0.269, p=0.039). Urinary Na-to-K ratio was not significantly associated with either PWV or AIx. By contrast, an inverse relationship was observed between urinary Na-to-K ratio and SEVR (r=-0.270, p=0.041). In multivariate analysis, urinary Na-to-K ratio was identified as an independent predictor of myocardial perfusion, as assessed by SEVR (beta=-0.233, p=0.047). Conclusions: This is the first study evaluating the association between urinary Na-to-K ratio and surrogate measures of vascular health in patients with RA. Findings from the present study suggest that excessive dietary intake of Na along with insufficient K consumption is highly prevalent in patients with RA. Consistent with population-based studies, urinary Na-to-K ratio might serve as an indicator of myocardial health in patients with autoimmune inflammatory diseases such as RA.