WHO/BS/2018.2339 WHO International Collaborative Study of the Proposed 2nd WHO IS for Free PSA

Overview

The World Health Organization (WHO) Expert Committee on Biological Standardization (ECBS) has recognized (2014) the need for a replacement International Standard (IS) for Free Prostate Specific Antigen (fPSA), 96/668, used for the calibration of immunoassays to measure fPSA in human serum. We report here, the evaluation of a candidate standard for fPSA by immunoassay by an international collaborative study carried out by ten laboratories in eight countries. The geometric mean of the laboratory estimates for the fPSA content of the current standard, 96/668, agreed with the assigned content of 1 µg/vial (1.057 µg/vial (95% CI 0.988 – 1.130, n=21, GCV 15.9% with a robust geometric mean of 1.045 µg/vial). The geometric mean of the laboratory estimates for the fPSA content of 17/102 was 0.545 µg/amp (95% CI 0.508 – 0.586, n=21, GCV 17.0%) with a robust mean of 0.533 µg/amp. This was supported by the ratio of estimates of 17/102 to 96/668 of 0.516 (95% CI 0.489 – 0.544, n=21, GCV 12.5%) with a robust mean of 0.512. These data support a value assignment of 0.53 µg/amp. The results of this study also indicate that the candidate standard appears sufficiently stable, on the basis of a thermally accelerated degradation study, to serve as an IS. The study included an assessment of the impact of the new standard on the routine measurement of fPSA in human serum samples. All laboratories contributed data during the collaborative study through the concomitant measurement of the fPSA immunoreactivity of fifteen human serum samples. The results indicate that the candidate standard is suitable for the continued calibration of immunoassay methods for the measurement of fPSA. Therefore, it is proposed that the candidate preparation in ampoules coded, 17/102 is established as the 2 nd IS for fPSA with an assigned content of 0.53 µg per ampoule.