Immunoturbidimetric measurement of cold insoluble globulin with reference to a laser nephelometric assay

A commercially available test kit for the kinetic immunoturbidimetric measurement of cold insoluble globulin was evaluated. The procedure is precise (CV intra-assay between 2.7 and 5.1%, CV inter-series 3.8%), simple, rapid, and can be fully mechanized. Antigen concentrations determined by both turbidimetry and laser immunonephelometry correlate with r= 0.94 (y = 0.96 x + 40.64). The detection limit is about 50 mg/1 fibronectin which is nearly 40 times higher than that of laser nephelometry. Improvements of the turbidimetric procedure are achieved by reduction of sample and reaction volume, higher predilution of antiserum, and by use of the peak rate modification (instead of fixed time) of the kinetic test. The peak rate version allows the determination of fibronectin in plasma within 3 to 5 min.