Standardization of two immunoassays for XXXX glandular kallikrein 2.

@entity1 @entity263 @entity14958 @entity535
BACKGROUND: Measurement of @entity1 kallikrein 2 ( @entity14958 ) has improved early detection and staging of @entity263 . However, reported concentrations of @entity14958 among currently used assays have not been standardized in any way. We compared two @entity14958 assays and five different recombinant @entity14958 variants (rhK2) and suggest a common calibrator as an important step and putative reference substance in @entity14958 assay standardization. METHODS: We measured 146 sera by two @entity14958 assays, using assay-specific calibrators to assess the difference between the two assays. Serial dilutions of five rhK2 preparations were measured repeatedly, with one preparation assigned as calibrator and the others as unknowns to define which variant provided the closest match between the two assays. This rhK2 variant was used to recalibrate both assays. We measured @entity14958 concentrations in the same 146 @entity1 to evaluate the change in the difference. RESULTS: Use of assay-specific calibrators for comparison of the two assays yielded a Deming regression equation of: y = 0.789 (95% confidence interval, 0.674-0.922)x + 0.014 (0.004-0.025) micro g/L; R(2) = 0.667. Analysis of five rhK2 variants revealed that the enterokinase (ek)-rhK2 form provided the best match between both assays. Using the ek-rhK2 as a common calibrator, we observed a change in the slope of the regression curve to: y = 1.106 (0.872-1.340)x + 0.006 (-0.002 to 0.016) micro g/L; R(2) = 0.648, suggesting an increase in the mean estimate of agreement between the two assays. CONCLUSION: Calibration with a common calibrator substantially increased agreement between the assays. The ek-rhK2 variant provided the best performance of all tested rhK2 variants and should undergo mass spectrometry and @entity535 analysis for exact mass determination and value assignment to evaluate its potential as a reference material for immunoassays for @entity14958 .
