Cystatin C

Cystatin C is a small protein produced by all nucleated cells at a steady rate, freely filtered by the kidney, and not significantly affected by muscle mass, diet, or sex. The eGFRcys equation uses it for an alternative GFR estimate.

Because production is independent of body composition, cystatin C-based eGFR is more accurate than creatinine-based eGFR in adults with extremes of muscle mass (athletes, frail elderly, amputees, sarcopenic). Combined creatinine + cystatin C estimates (eGFRcr-cys) are most accurate.

Healicus refers you to independent laboratories. You order from the lab; they take the sample, run it, and return your result on their own platform. Healicus never sees your value.

• Randox Health

  UK · EU · INTL

  Clinic-based premium panels — wider biomarker breadth than home-test brands.

  Visit Randox Health

• Synlab

  DE · EU · INTL

  Europe-wide medical lab network — referrals via partner GPs and direct-to-consumer programmes where offered.

  Visit Synlab

• Quest Diagnostics

  US

  Direct-to-consumer ordering via Quest's patient portal — same lab the US healthcare system uses.

  Visit Quest Diagnostics

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Reference values rise slightly with age. The eGFRcys calculation is the actionable output, not the raw cystatin C value.

Steroid therapy, thyroid dysfunction, and severe inflammation can elevate cystatin C independently of GFR.

• If your eGFR-creatinine is borderline, whether adding cystatin C clarifies your true kidney function.
• How body composition or recent dietary changes affect your interpretation.

1. [1]KDIGO 2024 Clinical Practice Guideline for CKD Evaluation(2024)