What is being tested?Cystatin C is a small protein that is produced by nucleated cells (those with chromosomes and genetic material at their centre, which is most of the body's cells). It is produced at a constant rate and is found in a variety of body fluids such as serum, spinal fluid, and breast milk.
Cystatin C is filtered out of the blood by the glomerulus - tiny blood vessels in the kidneys that allow water and dissolved substances and wastes to pass through their walls while retaining blood cells and larger proteins. What passes through the glomerulus forms a filtrate fluid. The rate at which this fluid is formed is called the Glomerular Filtration Rate (GFR). The kidney reabsorbs Cystatin C, glucose, and many other substances from the filtrate, while allowing waste products to be carried with the fluid to the bladder and eventually out of the body as urine.
