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PSA Standardization



Development of PSA Standards

Slide 16

October 2009

However, in 1995, Stamey and colleagues published an article showing that the extinction coefficient for PSA was actually 1.84 mL/mg/cm, and they determined this using quantitative amino acid analysis.  The previous extinction coefficient used for PSA standards with the Hybritech assay was 1.42 mL/mg/cm, approximately a 23% difference, with the Hybritech concentration reading higher than the more accurately determined standard. At that time Stamey hypothesized this finding would lead to the Hybritech Tandem-R assay reading 10-20% “too high.”  In 1999, the World Health Organization (WHO) established the First International Reference Preparation for PSA (WHO standards 96/670 for total and 96/668 for free PSA).  This standard is a recombinant DNA-derived human PSA, which was standardized using the new extinction coefficient.

Although many of the commercial PSA methods used at that time yielded values that were higher than the WHO-assigned value, very little attention came from the medical community about the potential impact of this new standard on prostate cancer screening.  Manufacturers then began to standardize PSA assays to the WHO standard, as recommended.  Finally, in 2003 it was noted that the change or differences between the Hybritech and WHO standards may have an effect on the medical decision levels.

Development of PSA Standards

 



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