Cystatin C is completely reabsorbed and catabolized in the proximal tubule; therefore, there is a negative correlation between eGFR and cystatin C. Important with respect to this study, low cystatin C has been proposed as a risk factor in healthy subjects for rapid kidney function decline [32] and is a risk factor for diabetic nephropathy [33]. This evidence concerns the gene CST3 and diabetic kidney disease.