[Studies of prostate-specific antigen (PSA) immunoassays--differences in characteristic of immunoreactivity and reference materials among the kits].

PURPOSE: We conducted this study to examine differences in characteristics of immunoreactivity for free PSA and alpha(1)-antichymotrypsin complex PSA (ACT-PSA) as well as in compositions and concentrations of PSA reference materials among commercially available PSA kits. METHODS: Fractionated serum samples using a Sephacryl S-200 column were measured by Tandem-R, Delfia-PSA, Ab bead PSA, ACS-PSA, Markit-M and gamma-seminoprotein (gamma-Sm) kits. The calibrators of Tandem-R, Delfia-PSA, Ab bead PSA and Markit-M were fractionated by the same method and measured by Tandem-R. The calibrators of Delfia-PSA, Ab bead PSA and Markit-M and control serums of ACS-PSA were measured by Tandem-R. RESULTS: Although the characteristic of immunoreactivity of Tandem-R, Delfia-PSA, and Ab bead PSA were found to be similar, they were not shown identical. ACS-PSA was proved to recognize free PSA greater than above three PSA kits, while Markit-M could scarcely detect free PSA. gamma-Sm recognized only free PSA. The calibrators of Tandem-R, Delfia-PSA, Ab bead PSA and Markit-M were proved to be only free PSA. The linear correlation was obtained between Tandem-R and Delfia-PSA or Ab bead PSA or Markit-M. The ratio of Delfia-PSA to Tandem-R, Ab bead PSA to Tandem-R and Markit-M to Tandem-R was 0.66, 0.93 and 2.2, respectively. With regard to relation of ACS-PSA and Tandem-R, two ratios of 0.22 and 0.25 were obtained between the two kits according to the different concentrations of control sera. CONCLUSION: The present studies suggest that the difference in PSA values among the commercial PSA kits results from (1) different characteristics of immunoreactivity for ACT-PSA and free PSA among PSA kits, (2) compositions of PSA calibrators among the kits, and (3) different concentrations of PSA calibrators among the kits.