Biomarker · Kidney
Cystatin C
Cystatin C is a blood marker used to estimate kidney filtration. How it compares with creatinine, why combining both can help, and what influences it.
Written by LON6EVITY Editorial Team · Last updated
What cystatin C is
Cystatin C is a small protein made by cells throughout the body and filtered by the kidneys. When kidney filtration falls, its blood level rises, so it can be used to estimate glomerular filtration rate (eGFR).
Why it is used alongside creatinine
Creatinine depends on muscle mass, which can make creatinine-based eGFR less accurate in people with very high or low muscle mass. A 2012 study in the New England Journal of Medicine (Inker et al.) found that an equation combining creatinine and cystatin C estimated GFR more accurately than either marker alone. NIDDK lists eGFR as a key test for chronic kidney disease.
Limitations
Cystatin C can be affected by factors other than kidney function, such as thyroid disorders and high-dose steroid use. It is not offered by every laboratory.
Reference ranges
Reference ranges differ between laboratories, units and methods, and depend on age, sex and your overall clinical picture. A single result is not a diagnosis — interpret it with a qualified clinician.
Factors that can affect the result
- Kidney function
- Thyroid disorders
- Corticosteroids
- Body composition
Questions people commonly ask
- Is cystatin C better than creatinine?
- Neither is perfect. Using both together generally gives a more accurate estimate than either one alone.
Related biomarkers
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Understand your biomarkers in context
What does this mean for your own health data? Log your results, follow trends over time and bring an organised summary to your next doctor's appointment.
Sources
- Estimating glomerular filtration rate from serum creatinine and cystatin C. Inker LA et al., N Engl J Med, 2012.
- Chronic Kidney Disease Tests & Diagnosis. National Institute of Diabetes and Digestive and Kidney Diseases (NIH).