Comment on: Richter et al. Serum Levels of the Adipokine Progranulin Depend on Renal Function. Diabetes Care 2013;36:410–414

Richter et al. (1) report an association between serum levels of the adipokine progranulin and chronic kidney disease (CKD) and demonstrate higher progranulin levels with deteriorating renal function—the highest progranulin levels being observed in stage 5 of CKD. The authors conclude that impaired renal clearance might account for this association and that their results are compatible with the hypothesis that renal filtration is an important route of progranulin elimination.

Confirmation of this interpretation, however, can only be obtained by either demonstrating lower urinary progranulin in association with lower estimated glomerular filtration rate, consistent with an accumulation of progranulin in the circulation, or by demonstrating that the renal arteriovenous concentration gradient is lower in CKD, indicative of reduced intrarenal metabolism or degradation.

The authors report significant amounts of progranulin in spot urine samples, which did not correlate with serum progranulin levels. Unfortunately, important information about the renal function of the subgroup in which this was tested is not presented in the article. It would be of great interest to analyze which stages of CKD were present in this subgroup and whether the authors attempted to test a possible correlation between urinary progranulin levels and total proteinuria.