Redesigned proficiency testing materials improve survey outcomes for prostate-specific antigen - A College of American Pathologists Ligand Assay Survey study

Context.-Large disparities in prostate-specific antigen (PSA) results from different assays have been observed in the College of American Pathologists (CAP) Ligand Assay Survey, with interassay results varying severalfold. Su rvey specimens are predominately composed of free PSA and do not reflect th e composition of typical patient specimens. Objectives.-To characterize a pilot material developed for CAP in which poo led sera samples were spiked with purified PSA and alpha (1)-antichymotryps in-bound PSA at targeted concentrations and to compare it to CAP survey and reference materials. Design.-CAP survey, reference, and pilot materials were analyzed using 10 t otal PSA and 7 free PSA assays. These assays included Food and Drug Adminis tration-approved assays and assays for research use only. Results.-Variability among the 10 total PSA methods was greatest for the 19 97 ligand survey material (CV range, 56%-65%) followed by the pilot materia l (CV range, 10%-29%) and the reference material (CV range, 6%-13%). In con trast, interassay variability for the 7 free PSA methods was similar for th e 3 preparations, with the exception of one specimen close to the limit of detection of the assays. As determined with the Hybritech Tandem-R method, the ligand survey specimens were essentially composed of all free PSA, wher eas the reference and pilot materials were composed of approximately 10% an d 35% free PSA, respectively. Conclusions.-The newly formulated pilot material prepared using a human bas e that contained defined concentrations of free PSA and alpha (1)-antichymo trypsin-bound PSA more closely resembled patient specimens and minimized di fferences among methods compared with the semen-supplemented original surve y material.