Patent ID: 7390677

Claim:
An immunoassay for assaying a target antigen or antibody present in serum or plasma portion of a whole blood sample, comprising the steps of: (a) mixing the whole blood sample with insoluble carrier particles which are sensitized with an antigen against the target antibody or an antibody against the target antigen, wherein said particles are smaller than erythrocytes, to cause an immune agglutination reaction resulting in an immune agglutination reaction mixture comprising agglutinated insoluble carrier particles and unagglutinated insoluble carrier particles; (b) introducing the immune agglutination reaction mixture to a flow cell, irradiating the particles passing through the flow cell with laser light, and detecting scattered light generated thereby; (c) setting a first threshold value for distinguishing unagglutinated insoluble carrier particles from agglutinated insoluble carrier particles and a second threshold value for distinguishing the agglutinated insoluble carrier particles from blood cells with regard to intensity of the scattered light; (d) distinguishing and counting the unagglutinated insoluble carrier particles, the agglutinated insoluble carrier particles and the blood cells from the intensity of the scattered light detected in the step (b), in reference to the first and second threshold values set in the step (c); (e) calculating a degree of agglutination from the number of the unagglutinated insoluble carrier particles and the number of the agglutinated insoluble carrier particles; (f) converting the degree of agglutination into a concentration of the target antigen or antibody in the whole blood sample using a calibration curve showing a relationship between a degree of agglutination and a concentration of a target antigen or antibody; and (g) obtaining a corrected concentration of the target antigen or antibody based on the following formula: C=CO /(1 −B/A ), wherein C is a corrected concentration, CO is the concentration of the target antigen or antibody present in the serum or plasma portion of whole blood sample, B is the number of blood cells and A is a constant.