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Biological variation of cystatin C: implications for the assessment of glomerular filtration rate
B G Keevil1, E S Kilpatrick, S P Nichols
1Department of Clinical Biochemistry, University Hospital of South Manchester, Wythenshawe Hospital, UK.
Insights
Serum cystatin C shows higher biological variability than serum creatinine, making it more sensitive for detecting early kidney function decline. However, serum creatinine remains better for monitoring changes in patients with existing kidney disease.
Area of Science:
- Nephrology
- Clinical Chemistry
- Biomarker Research
Background:
- Glomerular filtration rate (GFR) reduction is a key indicator of kidney disease.
- Accurate detection of mild to moderate GFR decline is crucial for timely intervention.
- Biological variability of kidney function markers influences their diagnostic utility.
Purpose of the Study:
- To compare the biological variability of serum cystatin C and serum creatinine.
- To assess the potential of these markers in detecting changes in glomerular filtration rate.
- To determine the suitability of each marker for different clinical scenarios.
Main Methods:
- Studied 12 healthy subjects to determine biological variation of serum cystatin C and creatinine.
- Accounted for analytical variation in the assessment of biological variability.
- Calculated interindividual and intraindividual variance for both markers.
- Determined critical differences for sequential measurements.
Main Results:
- Serum creatinine exhibited high interindividual variance (93%) and low intraindividual variance (7%).
- Serum cystatin C demonstrated lower interindividual variance (25%) and higher intraindividual variance (75%).
- Critical difference for significant change was 14% for creatinine and 37% for cystatin C.
Conclusions:
- Serum cystatin C's higher intraindividual variability suggests greater potential for detecting early GFR decline.
- Serum creatinine's lower intraindividual variability makes it more suitable for monitoring renal function in patients with established kidney disease.
- Both markers have distinct roles in assessing and monitoring kidney function.
Abstract:
To assess the inherent potential for detecting mild to moderate reductions in glomerular filtration rate, this study determined the biological variability of serum cystatin C and creatinine in 12 healthy subjects. After accounting for analytical variation, interindividual variance accounted for 93% and intraindividual variance accounted for 7% of serum creatinine biological variation. As such, to lie outside the assay reference interval, some subjects must exceed 13 SD from their usual mean value, whereas in others, a change of only 2 SD would be sufficient. For cystatin C, interindividual variation explained 25% and intraindividual variance explained 75% of biological variability. Therefore, the upper limit of the population reference interval for cystatin C is seldom more than 3-4 SD from the mean value of any healthy individual. The critical difference for sequential values significant at P < or = 0.05 was calculated as 37% for serum cystatin C and 14% for serum creatinine. We conclude that cystatin C is potentially a better marker for detecting impaired renal function than serum creatinine, but serum creatinine is probably still the better marker for detecting temporal changes of renal function in individuals with established renal disease.