Validation of Abbott Diagnostics turbidimetric cystatin C assay and enzymatic creatinine assay using the Architect c8000 analyzer

Abstract: Objective: Estimation of glomerular filtration rate (GFR) is an important tool in the diagnosis and management of chronic kidney disease. Today creatinine is the most frequently used marker for kidney function though several studies indicate that cystatin C is a superior marker. The purpose of this study was to validate Abbott Diagnostics turbidimetric cystatin C assay and enzymatic creatinine assay. Methods: The validation was performed by studies of CV for the two methods and correlations between the two and other available methods for assessing GFR. The stability of cystatin C at room temperature was also evaluated. Results: Both methods showed good precision. The Abbott cystatin C assay generally gave lower values and thereby higher estimated GFRs than the correlated Gentian method. The Abbott enzymatic creatinine assay gave higher values than the correlated Jaffe method. Those results are generally unexpected, but in this study the cause is an automatically applied negative intercept used together with the Jaffe method. Cystatin C showed high stability when stored at room temperature. Conclusions: Estimated GFRs tend to differ depending on the choice of method for analyzing cystatin C or creatinine and this study gives an overview of the range of variation. The study also enlightens the need for an international calibrator for the cystatin C methods presented by different manufacturers.