B-039 Method Performance Evaluation of the Siemens Atellica Cystatin C Assay on the CH930 Instrument
Authors: Maynard R , Korpi-Steiner N , Cotten S 
Published: September 2023

Abstract

Background
The National Kidney Foundation and American Society of Nephrology Task Force on Reassessing the Inclusion of Race in Diagnosing Kidney Disease published recommendations on the implementation of the CKD-EPI 2021 equation to calculate eGFRcr without a race coefficient. Clinical practice recommendations also suggest increasing availability of Cystatin C testing which can be a more reliable marker of renal function than creatinine for select adults with eGFRcr near medical decision points and in situations where non-GFR factors may have a large effect on serum creatinine. This study evaluated the method performance characteristics of the Cystatin C assay on the Siemens Atellica CH930 analyzer. The assay measures agglutination of latex particles coated with anti-cystatin C antibody at 571/805 nm and is approved for determination of Cystatin C in serum and plasma (lithium heparin, and EDTA).

Methods
Cystatin C reagent lot 2114231 and calibrator lot 560956 were used in the study. Intra-run precision was evaluated using BioRad IntelliQ Immunology Control (Level 1 lot 68991, Level 2 lot 68993). Inter-run precision was evaluated over 20 consecutive days. Mean, SD, and CV were calculated and compared to manufacturer precision claims in the IFU and BioRad UNITY™ Interlab Reports. Linearity was evaluated using AUDIT MicroControls Cystatin C Linearity LQ (Lot 06901). Accuracy was evaluated by measuring 40 serum samples on the Atellica CH930 and Roche Diagnostics Tina-Quant Cystatin C Gen 2 assay. Acceptable criteria were defined as a calculated slope between 0.9–1.1 and r greater than 0.995. Appropriateness of the adult reference interval was evaluated with 20 female and 20 male presumably healthy donors. Acceptability was defined as less than 10% of results outside the proposed range.

Results
Intra-run CV ranged from 2.3–9.2% (Level 1 QC) and 1.2–2.6% (Level 2 QC) across four different CH930 instruments. Level 1 precision did not verify the manufacturer claim of ≤3.6% CV on 3 out of 4 instruments. Level 2 precision did not verify the manufacturer claim of ≤1.7% CV for any instrument tested. Using BioRad UNITY™ peer performance as targets, 3 of 4 instruments had CV ≤6.7% for Level 1 and all instruments had CV ≤2.8% for Level 2. Inter-run precision for Level 1 QC was ≤5.94% CV which was less than the BioRad Peer Group CV. Linearity material spanned 0.490–5.893 mg/L and results were within manufacturer’s expected ranges. Method comparison with the Roche Tina-Quant Gen 2 assay had a calculated slope of 0.954, intercept of 0.094, and r value equal to 0.9993. Thirty-nine of 40 results were within 10% of the reference method (range 0.74–5.45 mg/L). Verification of the reference interval using presumably healthy donors resulted in 5.3% (2/38) of results outside the proposed range.

Conclusion
With the exception of precision, all other manufacturer-claimed performance specifications for the Siemens Atellica Cystatin C assay were verified using four CH930 instruments at our institution.