From the Guidelines
A cystatin C test is used to evaluate kidney function by measuring the level of cystatin C in the blood, providing an estimate of glomerular filtration rate (GFR) that is less affected by factors like age, sex, and muscle mass. This protein is produced at a constant rate by nearly all cells in the body and is filtered out by healthy kidneys, making it an excellent marker for GFR 1. The test is particularly useful for detecting early kidney disease or monitoring kidney function in people where creatinine tests might be less reliable, such as the elderly, children, or those with muscle wasting or unusual muscle mass. Some key points about cystatin C include:
- It is supposed to meet the criteria for an ideal GFR better than creatinine because it is produced at a constant rate, is not secreted, and is reabsorbed by tubule epithelial cells but subsequently catabolized so that it does not return to the blood flow 1
- Studies have shown cystatin C to be an accurate marker of subtle changes in GFR and diagnostically superior to creatinine with a significantly better correlation with GFR 1
- The test requires a simple blood draw and doesn't need any special preparation, with results typically interpreted alongside other kidney function tests to provide a comprehensive evaluation of kidney health
- Higher levels of cystatin C in the blood generally indicate decreased kidney function, as it means the kidneys aren't effectively filtering this protein from the bloodstream. The use of cystatin C as a marker can improve dose individualization for patients with reduced renal function receiving cytotoxic drugs, reducing the likelihood of toxicity 1.
From the Research
Cystatin C Test
The Cystatin C test is used to assess kidney function by estimating the glomerular filtration rate (GFR) [(2,3,4,5,6)].
Key Uses of Cystatin C Test
- To evaluate renal function and estimate GFR in patients with chronic kidney disease (CKD) [(2,3,4,5,6)]
- As a confirmatory test in clinical settings where the relationship between creatinine production and muscular mass impairs the clinical performance of creatinine 4
- To estimate and/or monitor renal function in children and adolescents due to rapid changes in muscle mass 4
- In patients with impaired muscle mass and in patients with an alteration of tubular secretion of creatinine 4
Advantages of Cystatin C Test
- Cystatin C has fewer non-GFR determinants compared to serum creatinine 5
- Use of serum cystatin C avoids the limitations related to both diet and muscle mass that affect serum creatinine 5
- Cystatin C may be more accurate than serum creatinine in estimating GFR [(5,6)]
- Cystatin C is more strongly associated with all-cause mortality and cardiovascular events 5
Limitations of Cystatin C Test
- Cystatin C testing availability is currently limited to primarily reference laboratories 2
- Assay standardization is needed to match the performance of creatinine assays 2
- Future research is needed to better understand the performance of cystatin C-based eGFR relative to creatinine-based eGFR and measured GFR in diverse cohorts 2