eGFR (cystatin C)

Like the creatinine eGFR, labs commonly print '>90' or '>60', and the value falls gradually with age in the general population.

This is an estimate of kidney filtering calculated from the cystatin C level rather than from creatinine, using the person's age and sex. Some labs combine cystatin C and creatinine in one formula. Because cystatin C does not depend on muscle mass, this estimate can differ from the creatinine-based eGFR in the same person.

Doctors request it to confirm or check a creatinine-based eGFR, particularly in people with unusually high or low muscle mass, in older age, or when the two tests disagree and a clearer picture is wanted.

• Low cystatin C from an underactive thyroid
• Pregnancy
• Recovery after a short-term kidney upset

• Long-term kidney disease
• An overactive thyroid or steroid tablets, which raise cystatin C
• Older age
• Smoking, being overweight and inflammation, by a small amount

• Thyroid activity and steroid medicines move cystatin C, and so this estimate, without any change in the kidneys
• Different labs use different formulas and assays, so numbers are not always comparable between labs
• The printed value is capped at '>90' or '>60' in many labs

Calculated from the cystatin C sample; no separate sample is needed. Best read side by side with the creatinine eGFR.

Written by a UK consultant physician. Typical UK adult reference ranges; your laboratory's own printed range takes precedence.