Background: Human cystatin C is a cysteine protease inhibitor produced by all nucleated cells in the body and the protein is present in all body fluids. The concentration in cerebrospinal fluid (CSF) is considerably higher than in plasma. Cystatin C levels seem to influence the development of Alzheimer disease (AD) and low levels in the brain are associated with an increased risk for AD. The aim of this study was to develop a high throughput assay for the quantification of cystatin C in CSF.
Methods: Antigen excess, imprecision, interference, linearity, recovery, sample stability and reference values were evaluated on Architect ci8200 (Abbott Laboratories, Abbott Park, IL, USA).
Results: The assay had an antigen-excess limit at 23 mg/L and was linear over the range of 0.84 to 8.33 mg/L. Results > 8.33 mg/L were automatically rerun in a higher dilution. Within-run coefficient of variation (CV) was 1.71, 1.10 and 0.79%, between day CV was 1.71, 0.39 and 1.45%, between-run CV was 0.58, 0.66 and 0.48%, and total CV was 2.49, 1.34 and 1.72% at cystatin C concentrations of 1.39, 3.17 and 6.28 mg/L, respectively. The recovery was 97-102%. No interference at a 7.5% deviation level was observed for 8.5 g/L of hemoglobin or 800 mg/L (1368 micromol/L) of bilirubin. Reference values for cystatin C in cerebrospinal fluid obtained with this method were 2.42-14.33 mg/L.
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