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 ( = 0.562,  < 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;  = 0.005), and showed an insignificant trend of predicting kidney event-free survival (adjusted HR, 1.36; 95% CI, 0.94-1.95;  = 0.10). Urinary podocin level by ELISA had a modest correlation with the rate of kidney function decline ( = 0.238,  = 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.