CST3 and Proteinuria: Proteinuria develops in the obese Zucker fa/fa rat already at around age 10 weeks [45] and decreased renal function is seen in obese Zucker fa/fa rats at around 12 weeks age [46], thus elevated urine concentrations (relative to creatinine) of total protein, free proteinogenic amino acids, cystatin C, carbamide and uric acid could be expected.