Improved immunoturbidimetric assay for cystatin C

An immunoturbidimetric assay for cystatin C was optimized with respect to assay imprecision. After investigating the optimum DH. polyethylene glycol concentration and specimen volume, two modifications were introduced: an increase in specimen volume to 25 muL; and an extension of the pre-incubation period to 240s. These modifications produced an assay with between-batch imprecision (coefficient of variation, n = 10 or 11) ranging from 3.9% at 0.72 mg/L to 1.3% at 5.29 mg/L The assay was susceptible to interference from lipaemia and haemolysis but not bilirubinaemia in both the original and modified protocol. Extending the pre-incubation to 240 s improved tolerance to common interferences and retained assay applicability in the routine clinical setting.