Serum phosphate varies with degree of proteinuria in nephrotic syndrome and is associated with elevated pulse wave velocity

Abstract

The occurrence of vascular stiffness in the setting of the nephrotic syndrome and the influence of serum phosphate on this association is unknown. A retrospective study of 42 prevalent, adult nephrotic patients who underwent carotid-femoral pulse wave velocity (PWV) measurement, a median of 24 months after kidney biopsy. Elevated PWV was determined using published age-specific reference ranges. The association, statistical significance and independence of serum phosphate with spot urine protein-creatinine ratio (PCR) and the association of phosphate with PWV was examined. Mean PCR was 5.5 g/g and mean eGFR (CKD-EPI) was 70 mL/min/1.73 m2. Serum phosphate was statistically significantly associated with severity of nephrotic syndrome independently of eGFR and age. Median (intra-quartile range) PWV was 7 m/s (4-11), with a linear trend for higher PWV across tertile of average serum phosphate over follow-up, P<.001. Twenty subjects (48%) had elevated age-specific PWV, which on logistic regression was statistically significantly associated with mean serum phosphate, OR (95% CI) per 0.1 mmol/L: 2.7 (1.5, 4.9), P = .001, which in separate analyses was independent of eGFR and other laboratory data. In this cohort of patients with the nephrotic syndrome serum phosphate was commonly elevated, despite well preserved eGFR, which was significantly and independently associated with elevated PWV over follow-up.