Standardization of Two Immunoassays for Human Glandular Kallikrein 2

has improved early detection and staging of prostate cancer. However, reported concentrations of hK2 among currently used assays have not been standardized in any way. We compared two hK2 assays and five different recombinant hK2 variants (rhK2) and suggest a common calibrator as an important step and putative reference substance in hK2 assay standardization. Methods: We measured 146 sera by two hK2 assays, using assay-specific calibrators to assess the difference between the two assays. Serial dilutions of five rhK2 preparations were measured repeatedly, with one prep-aration assigned as calibrator and the others as un-knowns to define which variant provided the closest match between the two assays. This rhK2 variant was used to recalibrate both assays. We measured hK2 con-centrations in the same 146 patients to evaluate the change in the difference. Results: Use of assay-specific calibrators for comparison of the two assays yielded a Deming regression equatio