Rapid quantification of prostate specific antigen (PSA) from fingerstick (FS) blood.
Authors: Thomas Joseph Earl , Srinivasan Balaji , Jacobs Nicole , Winkler Alfred , Zhao Zhen , Phillips Erica , Kensler Kevin , Tagawa Scott T. , Nauseef Jones T. , Molina Ana M. , Sternberg Cora N. , Sun Michael Philip , Scherr Douglas , Barbieri Christopher , Hu Jim , McClure Timothy D , Reckler Jon , Erickson David , Mehta Saurabh , Nanus David M. 
Published: January 2024

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Background: Screening for prostate cancer (PC) reduces PC-specific deaths. African American (AA) individuals have a ~2-fold higher risk of developing and dying from PC and may benefit from screening at a younger age. To increase access to PC screening for high-risk communities, we developed a portable, rapid point of care (POC) PSA test that quantifies PSA from FS blood in 20 minutes. We present preliminary data for our POC test. Methods: We developed a lateral flow immunoassay test strip1 combined with the Cube Reader (Chembio Diagnostics GmbH) to quantify PSA from FS blood. These measurements were compared on the same day with standard venous blood PSA as measured with the Siemens Centaur Chemiluminescent Immunoassay. Following informed consent, 50 µL of FS blood was mixed with 80 µL of buffer (PBS 1X with 1% Tween-20) and loaded onto the test strip. This ratio was found to be effective for adequate sample flow on the test strip. Eligible patients (pts) were undergoing standard of care PSA testing and had a recent PSA <20 ng/mL (to resemble a screening population). Pts with and without PC were included. Colorimetric signal intensities of the Test (T) and Control (C) lines were measured at 20 min with the Cube Reader. A scatter plot and Pearson correlation coefficient between the T/C ratios and the PSA results from venous blood were obtained for a group of 42 preliminary pts. A cohort of 30 pts additionally had 200 µL of FS blood (the minimum sufficient quantity) collected for serum analysis via the Centaur assay. This was done to evaluate for any unexpected variability between laboratory-based capillary and venous PSA results, and to test the feasibility of measuring PSA in the lab with a small volume of blood. Results: In these preliminary results, the 30 pts who had PSA measured from capillary and venous sera via the Centaur assay showed a correlation coefficient of 0.99. In the cohort of 42 pts who had PSA T/C ratios measured with the test strip, the correlation with venous PSA was 0.9. This encompassed a PSA range of 0.3-19.6 ng/mL with one outlier of 179 ng/mL. Based on a preliminary calibration curve from a small sample of 21 pts, the sensitivity and specificity of the POC test to detect a PSA >4 ng/mL was 100% (95% CI: 71.51-100) and 90% (95% CI: 55.50-99.75), respectively, in the 0.3-10 ng/mL detection range. Nineteen percent (8/42) of pts were AA. Conclusions: Serum from capillary and venous blood shows a strong correlation when measured via a standard laboratory assay. In addition, a rapid POC PSA test using a PSA test strip is easy to administer and preliminary data suggest a good correlation with standard venous PSA testing. The development of such a test may improve access to PC screening for high-risk individuals. Continued optimization and validation of our POC test is ongoing. 1. Curr Res Biotechnol 2021;3:288-299. Clinical trial information: N/A.