A 2026 study supports combining creatinine with cystatin C in some kidney assessments. Here is why one lab number needs context.
A creatinine result can look reassuring or worrying without telling the whole story. The eGFR on your report estimates how well your kidneys filter blood; it is not a direct measurement.
What is new?
A study published in The BMJ on 19 March 2026 examined three-year results from 875 adults with moderate chronic kidney disease in England. Equations combining creatinine and cystatin C tracked measured kidney-function changes more accurately than equations using one marker. But they were not perfect: at group level, all equations underestimated the decline over time, and none reliably identified every person whose disease progressed. The BMJ: Accuracy of GFR estimation for monitoring moderate CKD
Why muscle can change the picture
Creatinine is influenced by muscle as well as kidney filtration. High muscle mass, recent intense exercise or creatine supplements can raise it; low muscle mass can lower it. These influences may make creatinine-based eGFR look worse or better than actual kidney function. They are reasons to interpret a result carefully, not dismiss an abnormal one. National Kidney Foundation: Creatinine
Cystatin C is another blood marker that can help when creatinine is difficult to interpret. It also has limitations: untreated thyroid disease and steroid treatment can affect results. Combining markers can improve the estimate, but an extra test is not automatically necessary for everyone. National Kidney Foundation: Cystatin C
The practical takeaway
This England-based study does not establish identical accuracy for every Indian patient. Ask whether another marker would change your care. Kidney assessment also includes urine albumin-to-creatinine ratio, or uACR. Chronic kidney disease generally requires evidence persisting for at least three months; a new abnormal result still needs timely assessment. National Kidney Foundation: Best practices for CKD identification, risk stratification and management
Questions for your clinician
- Could my muscle mass, supplements or medicines affect this result?
- Would cystatin C change a treatment or dosing decision?
- Do I need a urine albumin test, and when should testing be repeated?
Start with our general KFT report guide for the basics of creatinine, urea and kidney health.
Sources and dates
- The BMJ: Accuracy of GFR estimation for monitoring moderate CKD — 19 March 2026
- National Kidney Foundation: Creatinine — updated 1 June 2023
- National Kidney Foundation: Cystatin C — updated 26 July 2023
- National Kidney Foundation: CKD identification and management — February 2026
Editorial/source check: 17 October 2026.
Medical disclaimer: Educational information only. A qualified clinician should interpret your results and guide testing or treatment. This article does not replace personalised medical advice.
© 2026 EndYourIllness. Original text. Third-party names and marks belong to their respective owners.
