Urinary and Kidney Podocalyxin and Podocin Levels in Diabetic Kidney Disease: A Kidney Biopsy Study

RATIONALE & OBJECTIVE: Diabetic kidney diseases (DKDs) are the most common cause of dialysis-dependent kidney disease around the world. Previous studies have suggested that urinary level of podocyte-associated molecules may predict the prognosis of DKD. STUDY DESIGN: Observational cohort. SETTING & PARTICIPANTS: 118 consecutive patients with biopsy-proven DKD; 13 nondiabetic patients with hypertensive nephrosclerosis as controls. PREDICTORS: Urinary podocalyxin and podocin levels were obtained by quantitative polymerase chain reaction and enzyme-linked immunosorbent assay (ELISA) and the corresponding intrarenal levels by western blotting. OUTCOMES: Dialysis-free survival; kidney event-free survival; rate of kidney function decline in 12 months. ANALYTICAL APPROACH: Correlation and time to event analysis. RESULTS: Urinary podocalyxin level was closely correlated with its messenger RNA (mRNA) level (r = 0.562, P < 0.001), but this did not predict the progression of DKD. Intrarenal podocalyxin level had only modest correlation with its urinary mRNA and ELISA levels, was an independent predictor of dialysis-free survival (adjusted HR, 1.85; 95% CI, 1.21-2.82; P = 0.005), and showed an insignificant trend of predicting kidney event-free survival (adjusted HR, 1.36; 95% CI, 0.94-1.95; P = 0.10). Urinary podocin level by ELISA had a modest correlation with the rate of kidney function decline (r = 0.238, P = 0.01) but did not predict dialysis-free survival. LIMITATIONS: Small sample size; lack of serial measurement. CONCLUSIONS: Intrarenal podocalyxin level, but not its urinary level, was an independent predictor of dialysis-free survival, whereas urinary podocin level by ELISA correlated with the rate of kidney function decline. Although intrarenal podocalyxin level has prognostic value, it may not be suitable for routine clinical use.