From the Guidelines
Cystatin C with eGFR is a valuable blood test for assessing kidney function, particularly in patients with unusual body compositions or those at risk for chronic kidney disease, as it provides a more accurate measurement of kidney function compared to traditional creatinine-based measurements alone, as recommended by the most recent guideline 1.
Key Points
- Cystatin C is a protein produced by all nucleated cells at a constant rate and freely filtered by the kidneys, making it a reliable marker of kidney function.
- The combination of cystatin C and creatinine in eGFR equations provides a more precise evaluation of kidney function, allowing for earlier detection of kidney disease and more accurate medication dosing, as supported by the KDIGO 2024 clinical practice guideline 1.
- The test requires a simple blood draw and no special preparation, with normal cystatin C levels typically ranging from 0.5 to 1.0 mg/L, and higher values indicating potential kidney dysfunction.
- This test is especially valuable for monitoring kidney function in patients with chronic kidney disease, diabetes, hypertension, or those taking medications that might affect kidney function, as emphasized by the American Journal of Kidney Diseases 1.
Clinical Recommendations
- In adults at risk for CKD, we recommend using creatinine-based estimated glomerular filtration rate (eGFRcr), and if cystatin C is available, the GFR category should be estimated from the combination of creatinine and cystatin C (creatinine and cystatin C–based estimated glomerular filtration rate [eGFRcr-cys]) 1.
- Cystatin C is recommended for confirmatory testing in specific circumstances when eGFR based on serum creatinine is less accurate, such as in individuals with low muscle mass, as suggested by the Diabetes Care guideline 1.
- The use of cystatin C-based eGFR (eGFRcys) is supported by evidence, particularly in persons without albuminuria or other markers of kidney damage, especially those with an eGFRcreat of 45 to 59 mL/min per 1.73 m2, as noted in the Annals of Internal Medicine 1.
From the Research
Definition of Cystatin C with eGFR
- Cystatin C is a filtration marker used to assess kidney function, providing an estimated glomerular filtration rate (eGFR) 2, 3, 4, 5, 6.
- eGFR is a measure of kidney function, calculated using serum creatinine or cystatin C levels, to diagnose and monitor chronic kidney disease (CKD) 2, 3, 4, 5, 6.
Advantages of Cystatin C with eGFR
- Cystatin C-based eGFR (eGFRcys) is a reliable and accurate marker of kidney function, correlating well with measured glomerular filtration rate (mGFR) 3, 4, 5.
- eGFRcys is particularly useful in patients where creatinine is an inadequate marker, such as those with muscle wasting diseases or malnutrition 3, 5.
- The combination of creatinine and cystatin C (eGFRcr-cys) provides a more accurate estimate of GFR than using either alone 2, 6.
Clinical Considerations
- Cystatin C eGFR can result in changes to CKD staging, with a substantial effect on patient management 4.
- Black race is associated with a lower likelihood of change to a later CKD stage using cystatin C eGFR, whereas age and comorbidities are associated with a higher likelihood of change 4.
- Clinicians should be informed about the impact of cystatin C eGFR on CKD staging and patient management 4.
Limitations and Future Directions
- Further research is needed to understand the performance of cystatin C-based eGFR in diverse populations and to achieve assay standardization 2, 3, 5.
- The availability of cystatin C testing needs to be broadened, and partnerships between clinical stakeholders and laboratories are necessary to promote its clinical use 2.