What is the significance of Cystatin C (Cysteine Proteinase Inhibitor C) in relation to Impaired renal function?

From the Guidelines

Cystatin C is a superior marker for estimating glomerular filtration rate (GFR) compared to creatinine, especially in patients with impaired renal function, due to its independence from age, sex, and muscle mass 1. The significance of Cystatin C in relation to impaired renal function lies in its ability to accurately estimate GFR, even in subtle changes, making it a valuable tool for diagnosing and monitoring kidney disease. Some key benefits of using Cystatin C include:

• It is produced at a constant rate by all nucleated cells in the body and freely filtered by the kidneys 1
• It is less affected by factors like age, sex, and muscle mass, which can influence creatinine levels 1
• It can be used alone or in combination with creatinine to calculate estimated GFR, providing a more accurate assessment of kidney function 1
• It has improved precision compared to creatinine, with less interassay variability 1 In clinical practice, Cystatin C can be particularly useful in:
• Elderly patients, where creatinine levels may be influenced by age-related muscle mass loss 1
• Patients with reduced muscle mass, where creatinine levels may not accurately reflect kidney function 1
• Individuals with early-stage kidney disease, where subtle changes in GFR may not be detected by creatinine alone 1 Overall, the use of Cystatin C as a marker for impaired renal function can improve dose individualization and reduce the likelihood of toxicity in patients receiving cytotoxic drugs 1.

From the Research

Significance of Cystatin C in Impaired Renal Function

• Cystatin C is a reliable and accurate marker of kidney function, especially in the early stages of chronic kidney disease 2, 3, 4, 5.
• It is produced at a constant rate by all nucleated cells and is freely filtered by the renal glomeruli, making it a suitable marker for glomerular filtration rate (GFR) estimation 3, 5.
• Cystatin C has several advantages over creatinine, including:
  • Independence from age, sex, and muscle mass 3, 5.
  • Ability to detect mild reductions in GFR 3.
  • Correlation with adverse outcomes compared to creatinine 2.
• The use of cystatin C is recommended by several guidelines, including the National Kidney Foundation and American Society of Nephrology Task Force, and the Kidney Disease Improving Global Outcomes (KDIGO) Clinical Practice Guideline 2, 4.
• Cystatin C can be used to estimate GFR in various populations, including pediatric and elderly patients, and in patients with malignant diseases or cardiovascular risk factors 5.
• However, there are also limitations to the use of cystatin C, including:
  • Variability in assay performance and standardization 2.
  • Limited availability of cystatin C testing in local laboratories 2.
  • Need for careful interpretation of cystatin C levels due to factors that can affect its concentration, such as thyroid dysfunction or glucocorticoids use 5.

Clinical Considerations

• Cystatin C can be used as a complementary biomarker to creatinine for kidney function assessment 2, 4.
• It is essential to consider the clinical context and population characteristics when interpreting cystatin C levels and estimating GFR 6.
• Further research is needed to fully understand the performance of cystatin C-based eGFR equations and to achieve widespread adoption of cystatin C in clinical practice 2, 4.