A-118 Evaluation of Mindray Cystatin C Assay

Abstract

Abstract Background Cystatin C is a low molecular weight non-glycosylated alkaline protein, with a molecular weight of 13kDa. It is formed by all nucleated cells in human at a constant rate. The only pathway of Cystatin C in vivo is excretion through glomerular filtration and absorbed by proximal renal tubular epithelial cells, which was decomposed finally. Therefore, the concentration of Cystatin C in serum is almost not affected by external factors, such as weight, age, gender, etc. Compared with creatinine and urea, it is an ideal endogenous marker for monitoring glomerular filtration function. Currently, the most methods on the market for testing Cystatin C are either latex enhanced immunoturbidimetric method, or immunoturbidimetric method. These methods usually use polyclonal antibodies from different animal species, which are sometime susceptible to the interference from rheumatoid factors reported in the literature, resulting in false positive results. The anti-RF interference ability of this reagent was enhanced by selecting the optimal antibody and optimizing reagent formulation. This study evaluated performances of the Cystatin C assay on Mindray BS-2000M system. Method Mindray Cystatin C assay is based on latex immunno-agglutination. Latex nanoparticles were coated with anti-Cystatin C antibody. Reagent of this assay contains R1 buffer and R2 with latex particles coupled with anti-Cystatin C antibodies. The assay starts with R1 and sample incubation for 5 min and then R2 is added. After another 5 min of incubation, agglutination occurs, leading to turbidity increasing. The turbidity is measured at 570 nm. Multi-level (5-point) calibration is used. Cystatin C concentrations are obtained from the calibration curve with signals from the assay with patient samples. Following basic assay performances were evaluated: precision, limit of detection, linearity, method comparison, interference and high dose hook. Results The precision study followed EP05-03 protocol. The repeatability and within-lab CVs on the BS-2000M system with 2 QC and 3 patient samples were ranged from 0.9% to 5.3%, respectively. Limit of detection was 0.1 mg/L and linearity was given up to 8.63 mg/L. The assay (y) shows good accuracy when compared with Roche Cystatin C (x) assay on the cobas 701: y = 1.0055x - 0.0268 (r2 = 0.9994, n = 109). The assay showed no significant with bilirubin up to 40 mg/dL, with hemoglobin up to 500 mg/dL, with lipids up to 500 mg/dL, and with rheumatoid factors up to 1200 IU/mL that is about 0.3% out of a total of 55 184 samples collected from our customers in China with RF measurements. No prozone was observed with the assay up to the high cystatin C concentration of 800 mg/L tested. Conclusion From this evaluation, we confirmed that Mindray Cystatin C assay can measure serum Cystatin C precisely and accurately, and with good performance against rheumatoid factors interference. It is suitable for use in routine clinical laboratories.