From the Guidelines
For the most accurate assessment of kidney function, using both cystatin C and creatinine-based estimated glomerular filtration rate (eGFRcr-cys) together is recommended, as it provides better precision than either alone, especially in patients with muscle wasting, liver disease, or those who are elderly, obese, or malnourished 1.
Key Differences Between Cystatin C and GFR
- Cystatin C is a protein produced by all nucleated cells at a constant rate and is freely filtered by the kidneys, making it a more accurate marker of kidney function than creatinine in certain populations.
- GFR is the actual rate at which the kidneys filter blood, typically measured in mL/min/1.73m².
- Cystatin C is less affected by muscle mass, diet, or medications than creatinine.
Clinical Recommendations
- The 2021 CKD-EPI creatinine equation refit without the race variable is recommended for initial assessment of GFR in U.S. adults 1.
- Cystatin C-based GFR calculations (eGFRcys) are particularly valuable for patients with muscle wasting, liver disease, or those who are elderly, obese, or malnourished, where creatinine-based measurements may be less reliable.
- Using both markers together (eGFRcr-cys) provides better precision than either alone and is especially useful when making critical clinical decisions about medication dosing, contrast administration, or diagnosing chronic kidney disease in patients with borderline results from standard testing 1.
Important Considerations
- Cystatin C may detect kidney dysfunction at an earlier stage than creatinine in people with diabetes 1.
- The combined approach of using both cystatin C and creatinine-based estimated glomerular filtration rate (eGFRcr-cys) is supported by recent guidelines and recommendations 1.
- Clinical laboratories should implement laboratory standards of care to ensure accuracy and reliability when assessing GFR using creatinine and cystatin C 1.
From the Research
Comparison of Cystatin C and Glomerular Filtration Rate (GFR) in Assessing Renal Function
- Cystatin C is a low molecular weight protein that can be used as an alternative to serum creatinine for estimating GFR, as it is less influenced by factors such as inflammation, infections, and dietary habits 2.
- Studies have shown that cystatin C-based equations can provide a more accurate estimation of GFR, especially in certain populations such as children and young adults with chronic kidney disease (CKD) 3.
- The Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) serum creatinine eGFR equation has been updated to exclude the race variable, and the CKD-EPI creatinine-cystatin C equation has demonstrated the highest reliability 4.
- Cystatin C has been shown to enhance GFR estimating equations in kidney transplant recipients, with the equation incorporating both cystatin C and creatinine performing better than those using creatinine or cystatin C alone 5.
- A comparative analysis of serum cystatin C and serum creatinine based estimating equations in type 2 diabetes found that the CKD-EPI equation derived eGFR had the best correlation with albumin excretion rate (AER) and identified the maximum number of patients in the normo-albuminuria group as having CKD 6.
Key Findings
- Cystatin C-based equations can provide a more accurate estimation of GFR in certain populations.
- The CKD-EPI creatinine-cystatin C equation has demonstrated the highest reliability.
- Cystatin C can enhance GFR estimating equations in kidney transplant recipients.
- The CKD-EPI equation derived eGFR has the best correlation with AER in type 2 diabetes.
Equation Performance
- The CKiD U25-CysC equation had the overall best performance compared to measured GFR (mGFR) in a pediatric population 3.
- The CKD-EPI-Creat+CysC equation was most precise and reflected GFR change over time reasonably well in kidney transplant recipients 5.
- The CKD-EPI equation identified the maximum number of patients in the normo-albuminuria group as having CKD in type 2 diabetes 6.