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Reference intervals for serum cystatin C in healthy Mexican adults

Glomerular filtration rate (GFR) remains the most accurate predictor for assessing kidney function. Serum creatinine levels are currently used to assess renal function, but this method has some important limitations, mainly because creatinine is filtered by the glomerulus and is secreted by the proximal tubules, and the level of serum creatinine depends on muscle mass and meat intake. Furthermore, the level of serum creatinine increases only when renal failure is in an advanced stage (1). GFR can also be measured by subcutaneous or intravenous administration of substances labeled with radioactive isotopes, such as wCx-inulin, which is considered a standard reference. However, these tests are too complex and laborious for routine clinical application (2). Cystatin C (CysC) is produced by nucleated human cells and its concentration does not change in systemic inflammatory processes. Glomerular filtration eliminates CysC from the bloodstream, and because CysC is a non-glycosylated low-molecular weight protein with an isoelectric point of approximately 9, it is freely filtered by the glomeruli. There is a strong correlation between high levels of CysC in serum and renal damage, so CysC has been suggested as an ideal endogenous marker to detect subclinical kidney disorders (3–7). High concentrations of this protein have also been associated with an increase in the incidence of tumors, neurological disorders, and conditions related to renal damage (8). However, information available on reference values for serum