Cystatin C

What it measures

Cystatin C is a small protein produced by all nucleated cells and filtered freely by the glomerulus. Because it is little affected by muscle mass, it provides an alternative marker for estimating GFR.

Specimen and preparation

• Specimen: Serum or lithium-heparin plasma
• Tube: Gold top

Reference range

Reference ranges differ between laboratories, methods and populations. Always use the range printed on your own lab report.

Causes of high values

• Reduced GFR (acute or chronic kidney disease)
• Hyperthyroidism
• High-dose corticosteroids
• Inflammation and smoking (mild)

Causes of low values

• Hypothyroidism

Method

Particle-enhanced immunoturbidimetry or nephelometry

Good to know

Use with creatinine in the combined CKD-EPI equation to confirm CKD stage, especially when muscle mass is unusual.

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