Development of microplate immunoassay methods for the measurement of prostate specific antigen and its [alpha1antichymotrypsin complex in serum.

The measurement of prostate specific antigen (PSA) is used as both a screening test for prostate cancer and for monitoring treatment of the disease. Although several methods have been developed to measure PSA, the results produced are not equivalent for all samples and assay methods. These problems are caused by differences in antibody affinity for the different forms of PSA present in serum and difference in the composition of the calibrator used for each assay. Methods for quantification of PSA that are not affected by these problems were developed. Two assays were developed, a total PSA assay and an assay specific for PSA complexed of alpha1-anatichymotrypsin (PSA-ACT). The antibodies selected for the assays demonstrate similar affinity for both forms of PSA. Pooled sera containing approximately 95% PSA-ACT complex and 5% free PSA was used as a calibrator in order to closely match the immuno-reactivity and PSA composition of serum samples. The test format selected for total PSA assay uses polyclonal anti- PSA antibodies coated on the solid phase and monoclonal anti- PSA antibodies for quantification. Two different sample volumes, 5 and 50 micro liters each were used for the assay. The total PSA assay has a reportable range from zero to 500 ng/mL. The sensitivity is 0.06 ng/mL. The within day precision is 5% calculated as the percent coefficient of variation for samples between 4 and 12 ng/mL. The run to run precision is less than 10%. No hook effect was seen in either assay for samples with concentrations up to 15,000 ng/mL. The total PSA results correlate well with the Hybritech Tandem E. PSA kit producing a correlation coefficient of 0.996 and a slope of 0.927. These results demonstrate that the total PSA assay is satisfactory for use in the clinical laboratory. The PSA-ACT specific assay also correlates will with the Hybritech E PSA and is a possible replacement for the total PSA assay.