Cystatin C

A protein filtered by the kidneys that helps estimate filtration. It is less influenced by muscle mass than creatinine; combining both markers often improves the estimate.

CYCC

Kidney Function

Measured in mg/L

What it measures

Cystatin C is a protein produced by nucleated cells and filtered from blood by the kidneys. Its blood concentration can be used to estimate filtration. It is less influenced by muscle mass than creatinine, making it useful when creatinine is difficult to interpret.

Cystatin C is not a perfect or universally superior marker. Thyroid dysfunction, steroid medicines and other non-kidney factors can influence it. A change should therefore be interpreted alongside clinical context.

An equation combining creatinine and cystatin C generally gives a more accurate estimate than either marker alone. A clinician can decide which estimate is appropriate and consider it alongside urine tests and changes over time.

Quick facts

Code: CYCC
Unit: mg/L
Category: Kidney Function

Related markers

Creatinine(CREA)Estimated GFR(GFR)

What your results mean

Low

Below Range

A low cystatin C level generally indicates that your kidneys are filtering very efficiently. It can also be lower in people with an underactive thyroid. If you have any concerns, your GP can advise.

Normal

Within Range

Your cystatin C level is within the healthy range, which is consistent with normal kidney filtration. It is less influenced by muscle mass than creatinine, which makes it useful when creatinine is hard to interpret.

High

Above Range

A raised cystatin C level may suggest that your kidneys are not filtering quite as efficiently as expected. However, a single result does not define your kidney health, and levels can fluctuate. Your GP can review this alongside your creatinine and GFR results to build a more complete picture, and may suggest a follow-up test to track trends.