From the Guidelines
Cystatin C is a crucial marker for assessing impaired renal function, particularly in situations where creatinine-based estimates may be misleading, and its use is recommended for confirmatory testing in specific circumstances, such as in individuals with low muscle mass or those at risk for or with chronic kidney disease 1.
Importance of Cystatin C in Renal Function Assessment
Cystatin C is a protein produced by all nucleated cells in the body that serves as a reliable marker for kidney function. It is filtered freely by the glomeruli and almost completely reabsorbed and metabolized by the proximal tubular cells, making it an excellent indicator of glomerular filtration rate (GFR). Unlike creatinine, cystatin C levels are not significantly affected by muscle mass, age, gender, or diet, providing a more accurate assessment of kidney function in certain populations such as the elderly, children, or those with reduced muscle mass.
Clinical Utility of Cystatin C
Cystatin C testing is particularly useful when creatinine-based estimates of GFR may be misleading, such as in patients with liver disease, malnutrition, or amputation. Normal cystatin C levels typically range from 0.5 to 1.0 mg/L, with higher values indicating decreased kidney function. Equations that combine cystatin C with creatinine often provide the most accurate GFR estimates, as highlighted in the KDIGO 2024 clinical practice guideline for the evaluation and management of chronic kidney disease 1. The use of cystatin C in combination with creatinine is recommended for specific situations, such as in individuals with low muscle mass or those at risk for or with chronic kidney disease.
Key Considerations for Cystatin C Use
Some key points to consider when using cystatin C for renal function assessment include:
- Cystatin C levels are not significantly affected by muscle mass, age, gender, or diet
- Cystatin C testing is particularly useful when creatinine-based estimates of GFR may be misleading
- Equations that combine cystatin C with creatinine often provide the most accurate GFR estimates
- The use of cystatin C in combination with creatinine is recommended for specific situations, such as in individuals with low muscle mass or those at risk for or with chronic kidney disease 1 In clinical practice, the use of cystatin C as a confirmatory test can help improve the accuracy of renal function assessment, particularly in high-risk populations, and inform critical decisions about medication dosing or evaluating early kidney disease 1.
From the Research
Significance of Cystin C in Renal Function
- Cystatin C is a useful marker for assessing renal function, particularly in the early stages of chronic kidney disease (CKD) 2, 3, 4, 5, 6
- It is not affected by muscle mass, diet, or gender, making it a more accurate marker than serum creatinine in certain populations, such as the elderly, diabetics, and those with varying muscle mass 2, 4, 6
- Cystatin C is a better predictor of CKD than creatinine in stages with eGFR ≥ 60 ml/min/1.73 m2, as it can detect mild to moderate impairment of kidney function more accurately 2
Comparison with Serum Creatinine
- Serum creatinine remains within normal levels until a significant reduction in renal function has occurred, whereas cystatin C can detect early renal dysfunction 2
- Cystatin C is more sensitive than serum creatinine in detecting early renal dysfunction, particularly in patients with eGFR ≥ 60 ml/min/1.73 m2 2, 4
- However, serum creatinine is still a useful marker, and the combination of both cystatin C and creatinine can provide a more accurate assessment of renal function 2, 5
Clinical Applications
- Cystatin C should be considered as a screening tool for early renal impairment, particularly in patients with hypertension, diabetes, and other conditions that increase the risk of CKD 2, 4
- The use of cystatin C can improve the detection of harmful acute and chronic changes in kidney function, and can help reduce healthcare inequalities 4
- Cystatin C can also be used to improve the precision of treatment eligibility and safety, and to monitor disease progression in patients with CKD 4, 5