Cystatin C, Human urine

Cystatin C is a marker for allograph function in adult transplant patients. Cystatin C regulates extracellular cysteine protease activity, which results from microbial invasion or release of lysosomal proteinases from dying or diseased cells. It is freely filtered by the glomerular basement membrane (GBM) and serum concentration has been shown to correlate well with glomerular filtration rate (GFR).