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Published on: March 17, 2010
Systematic shifts in cystatin C between 2006 and 2010
David M Maahs1, Diana Jalal, Kim McFann
1Barbara Davis Center for Childhood Diabetes, University of Colorado-Denver, PO Box 6511, Mail Stop A140, Aurora, CO 80045, USA. David.Maahs@uchsc.edu
Summary
Cystatin C assay results showed a decrease over time, indicating assay drift. Regression adjustment can correct these systematic shifts, highlighting the need for standardization.
Area of Science:
- Biochemistry
- Clinical Chemistry
- Nephrology
Background:
- Cystatin C is an emerging biomarker for assessing renal function.
- Standardization of cystatin C assays remains a challenge.
- Assay drift can impact the reliability of longitudinal studies.
Purpose of the Study:
- To compare cystatin C measurements over time within the Coronary Artery Calcification in Type 1 Diabetes (CACTI) study.
- To evaluate for potential assay drift in repeated measures of cystatin C.
- To assess the impact of assay changes on biomarker interpretation.
Main Methods:
- Serum samples from three visits (2000-2008) were analyzed in the same laboratory at different times (2006, 2007-2008, 2010).
- Dade-Behring assay was used for cystatin C measurement.
- Statistical analyses included regression and Bland-Altman plots to assess changes over time.
Main Results:
- Mean cystatin C levels demonstrated a decrease over the study period (V1: 0.80, V2: 0.75, V3: 0.69).
- Remeasured samples from earlier visits (V1, V2) showed significantly lower values compared to later measurements.
- Strong correlations between original and re-run values were observed, but systematic shifts were evident.
Conclusions:
- Systematic shifts in cystatin C measurements occurred over time in the laboratory.
- These shifts can be corrected using regression adjustment.
- The findings underscore the critical need for cystatin C assay standardization and improved measurement reliability.
