Bishop Clinical Chemistry Practice Test

Cystatin C is produced by all nucleated cells at a constant rate. This broad, steady production means its blood level reflects how well the kidneys are filtering, rather than being tied to a specific organ. Because it is freely filtered by the glomerulus and not significantly secreted or reabsorbed, serum cystatin C serves as a useful endogenous marker of glomerular filtration rate. Red blood cells lack a nucleus, so they do not produce cystatin C, which helps explain why production isn’t tied to them.