Measurement of circulating forms of prostate-specific antigen in whole blood immediately after venipuncture: Implications for point-of-care testing

Background: The purpose of this study was to validate the use of whole-bloo d samples in the determination of circulating forms of prostate-specific an tigen (PSA). Methods: Blood samples of hospitalized prostate cancer and ben ign prostatic hyperplasia patients were collected and processed to generate whole-blood and serum samples. Three different rapid two-site immunoassays were developed to measure the concentrations of total PSA (PSA-T), free PS A (PSA-F), and PSA-alpha (1)-antichymotrypsin complex (PSA-ACT) to detect i n vitro changes in whole-blood samples immediately after venipuncture. The possible influence of muscle movement on the release of PSA from prostate g land was studied in healthy men by measuring the rapid in vitro whole-blood kinetics of PSA forms before and after 15 min of physical exercise on a st ationary bicycle. Results: Rapid PSA-T, PSA-F, and PSA-ACT assays were designed using a 10-mi n sample incubation. No significant changes were detected in the concentrat ions of PSA-T, PSA-F, and PSA-ACT from the earliest time point of 12-16 min compared with measurements performed up to 4 h after venipuncture. Physica l exercise did not influence the concentrations of the circulating forms of PSA. Hematocrit-corrected whole-blood values of PSA-T and PSA-F forms were comparable to the respective serum values. Calculation of the percentage o f PSA-F (PSA FIT ratio x 100) was similar irrespective of the sample format used, i.e., whole blood or serum, Conclusions: We found that immunodetectable PSA forms are likely at steady state immediately after venipuncture, thus enabling the use of anticoagulat ed whole-blood samples in near-patient settings for point-of-care testing, whereas determinations of PSA (e.g., PSA-T, PSA-F, or PSA-ACT) performed wi thin the time frame of the office visit would provide results equivalent to conventional analyses performed in serum. (C) 2001 American Association fo r Clinical Chemistry.