Assessment of Agreement between Two Difference Prostate-Specific Antigen Assay Modalities

SIMPLE SUMMARY: Prostate-specific antigen is a biomarker for prostate cancer. If the level of prostate-specific antigen is high, a prostate biopsy is needed to diagnose prostate cancer. However, the definite level of prostate-specific antigen that requires prostate biopsy has not been established. Currently, there are many kinds of assay modalities that have been used for prostate-specific antigen testing. This study was conducted under the hypothesis that there will be differences between different assay modalities; therefore, there is no definite prostate-specific antigen level for prostate biopsy. In our study, the level of prostate-specific antigens was measured in one blood sample per patient, with two different assay modalities in 4810 patients. As a result, we confirmed that the overall agreement between the two modalities is excellent, but the agreement is slightly different in some ranges that may give clinical significance. Accordingly, the conformity between each assay modality should be secured in the future, and the threshold for the level of prostate-specific antigens for biopsy by each assay modality should be independently determined. ABSTRACT: There is controversy over the usefulness of prostate-specific antigen (PSA) as a prostate cancer (PCa) biomarker. This controversy arises when there are differences in the results of PSA assay modalities. In this study, which aimed to evaluate a proper validation between the two PSA assay modalities, the agreement between the results of the two modalities was analyzed. PSA examinations were conducted using two PSA assay modalities in 4810 patients. The intra-class correlation coefficient (ICC) and weighted kappa analysis were used to evaluate the agreement between the two assay modalities. A linear regression was performed to evaluate the association between the two assay modalities. According to ICC values (ICC: 0.999, p < 0.001) and weighted kappa analysis values (kappa: 0.951, alpha’s standard error (ASE): 0.001, p < 0.0001), the agreement between the assay modalities was rated as excellent. However, the strength of agreement was poor in the following PSA sub-groups: 0.05–0.1 ng/mL (ICC: 0.281, p = 0.0860); 0.15–0.2 ng/mL (ICC: 0.288, p = 0.0036); 1.5–2.0 ng/mL (ICC: 0.360, p = 0.0860); and 2.0–2.5 ng/mL (ICC: 0.303, p = 0.0868). In linear regression analysis, when modality B PSA yielded a value of 0.2 ng/mL, the expected value for modality A was 0.258 ng/mL (95% CI: 0.255–0.260), and when modality B PSA yielded a value of 4 ng/mL, the expected value for modality A was 3.192 ng/mL (95% CI: 3.150–3.235). The difference in the PSA values between the two PSA assay modalities is confirmed, and this difference may be clinically meaningful.