GFR Estimation After Cystatin C Reference Material Change

Area of Science:

• Clinical Chemistry
• Nephrology
• Pediatric Medicine

Background:

• Glomerular filtration rate (GFR) is commonly estimated using cystatin C.
• The International Federation of Clinical Chemistry (IFCC) introduced a standardized cystatin C reference material in 2010, leading to new estimation equations.
• Siemens transitioned to IFCC-calibrated kits in 2018, necessitating an evaluation of their impact.

Purpose of the Study:

• To assess the effect of IFCC calibration on cystatin C measurements.
• To evaluate the impact of IFCC calibration on estimated GFR (eGFR) equations in pediatric patients.

Main Methods:

• Cystatin C was measured in 81 pediatric patients using plasma samples.
• Paired cystatin C concentrations were determined using both nonstandardized and IFCC-standardized Siemens kits.
• GFR-estimating equations were compared using Bland-Altman analysis before and after IFCC standardization.

Main Results:

• The IFCC-standardized assay showed a mean increase of 24% in measured cystatin C values.
• Pre-standardization equations consistently overestimated GFR.
• Post-standardization, the Full Age Spectrum equation performed best overall, while the Chronic Kidney Disease in Children (CKiD) equation was more accurate for reduced GFR.

Conclusions:

• IFCC standardization significantly increased cystatin C values and altered GFR estimation equation performance.
• Clinical laboratories and healthcare providers may need to update their GFR estimation equations following the adoption of the IFCC standard.