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

Background: The occurrence of vascular stiffness in the setting of the nephrotic syndrome and the influence of serum phosphate on this association is unknown. Methods: 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. Results: Mean PCR was 5.5 g/g and mean eGFR (CKD-EPI) was 70 mL/min/1.73m². 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. Conclusions: 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.