Comparison by LC-MS and MALDI-MS of prostate-specific antigen from five commercial sources with certified reference material 613

Use of many of the commercial PSA sources as authentic PSA standards for calibrants for in vitro diagnostic tests could lead to significantly biased PSA measurements. Although all the PSA samples appear to be relatively stable for the time periods and conditions studied, some of the commercially available samples contain limited amounts of PSA and included other unidentified components.