Development of Latex Photometric Immunoassay of Serum CA 19-9 Applicable to Conventional Clinical Chemistry Analyzers

In order to establish a speedy and convenient assay of serum CA 19-9, we developed a latex photometric immunoassay of the antigen. Latex reagent was prepared by physical binding of F(ab')2 fragment of murine monoclonal antibody (1116 NS 19-9) onto latex particles. Latex reagent showed dose-dependent agglutination after being mixed with CA 19-9 antigen. The latex assay required only 10 minutes and could be automated by using conventional clinical chemistry analyzer, COBAS MIRA. Intensity of signal of the reaction could be adjusted by modifying the concentration of reaction accelerating polymer, polyvinyl pyrrolidone K90 (PVP K90). When we used the assay buffer containing 2 g/l of PVP K90, minimum detection dosage was 2 units/ml and measuring range was up to 400 units/ml; they were similar to those of radioimmunoassav (RIA) and enzyme immunoassay (EIA). Within and between assay precisions were both about 5% in coefficient of variation (CVI at normal ranae and about 1-2% in CV at increased level. Correlation versus commercially available EIA was y(Latex assay)=1.08x(EIA)+ 3.41, r=0.981(n=101). Prozone phenomenon could be detected by utilizing mechanism of the instrument. These results indicate that this assay can be applied to daily analysis in clinical laboratories as a speedy and convenient substitute of RIA and .EIA.