Cystatin C

What is Cystatin C?

Cystatin C is a small protein produced by all cells with nuclei that serves as an alternative marker for kidney function. Unlike creatinine, it’s not affected by muscle mass, age, sex, or race, making it particularly useful for assessing kidney function in elderly patients, children, and people with unusual muscle mass.

Why is it Tested?

Doctors order cystatin C when creatinine results may be misleading, such as in elderly patients with low muscle mass or bodybuilders with high muscle mass. It’s also used to detect early kidney disease when creatinine is still normal and to calculate more accurate eGFR in certain populations.

Normal Ranges

What do Abnormal Results Mean?

Abnormal results are not a diagnosis. Always discuss your results with a qualified healthcare provider before making any medical decisions.

Low Cystatin C

Low levels are uncommon and may indicate:

• Hyperthyroidism
• Certain genetic variants
• Pregnancy (due to increased kidney filtration)

High Cystatin C

Elevated cystatin C indicates reduced kidney function and may point to:

• Chronic kidney disease
• Acute kidney injury
• Cardiovascular disease risk
• Hypothyroidism (mild elevation)

How to Track Over Time

Cystatin C tracking provides a muscle mass-independent view of kidney function over time. It often rises before creatinine in early kidney disease, making it valuable for detecting subtle kidney function decline. Combined with creatinine, it offers a more complete picture of kidney health than either marker alone.