Modified anti-human ALB antibody and horseradish peroxidase labeled avidin. The anti-human ALB antibody binds to the human ALB bound to the coated antibody, and the biotin specifically binds to avidin to form an immune complex in which the free components are washed away. Color substrate (TMB) is added, TMB is blue under the catalysis of horseradish peroxidase, and becomes yellow with the addition of termination solution. The CONCENTRATION of ALB in the sample is calculated by drawing a standard curve.