An enzyme-linked immunosorbent assay (ELISA) for prostate-specific antigen

A sandwich ELISA for human prostate-specific antigen (PSA) is described. Optimal assay conditions, resulting in a sensitive assay with a low background, are presented. The method uses a hyperimmune antiserum produced in the New Zealand white rabbit, against human semen PSA. The IgG fraction of the antiserum was conjugated with horseradish peroxidase and used in the sandwich ELISA method. The anti-PSA IgG showed no cross reactions with saliva, normal blood, female urine, vaginal fluid, or menstrual blood. On occasions, a blood sample showed a non-specific cross-reaction, which was detected by non-immune rabbit IgG. This reaction could be caused by rheumatoid factors, as indicated by experiments with a series of known IgG and IgM rheumatoid antibodies, although other heterophilic antibodies could not be eliminated. The recovery of PSA added to blood plasma, saliva and vaginal fluid was affected by three factors; (a) protein concentration (dilution) of body fluid; (b) nature of the protein; and (c) amount of PSA added.