cystatin c

An effective measurement alternative

The best indicator of overall kidney health and function is glomerular filtration rate (GFR). Creatinine, the most common serum marker used to assess GFR, can present problems due to variability in creatinine formation among individuals as well as tubular secretion. An alternative way to accurately assess GFR is by measuring serum cystatin C.

Cystatin C test menu

Cystatin C

Cystatin C is similar to creatinine in that it is produced at a constant rate and is freely filtered by the glomerulus. However, unlike creatinine, cystatin C is not solely produced in muscles and consequently, not linked to skeletal muscle mass. As a result, serum cystatin C correlates more closely to GFR than serum creatinine, especially in patients with atypical muscle mass. Race does not appear to greatly impact cystatin C serum concentrations. Thus, race isn’t required for calculating an estimated GFR using cystatin C.

Key testing


  • Provides an index of glomerular filtration rate.
  • Estimates glomerular filtration rate in patients presenting with:
    • Abnormal muscle mass (e.g., obesity and malnourishment).
    • Rapidly changing muscle mass (e.g., hospitalized patients).
  • Confirms or refutes an abnormal creatinine-estimated GFR.

When to consider testing

Use the CKD-EPI cystatin C equation to estimate GFR for patients when creatinine may mislead.

  • For adults, estimated GFR is calculated using the CKD-EPI cystatin C (2012) equation.
  • For pediatrics, estimated GFR is calculated using the SchwartzCysC (2012) equation.

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