Prostate specific antigen (PSA) screening from fingerstick blood: Initial validation of a point-of-care (POC) test.

Abstract

e17164 Background: Prostate cancer (PC) is the most common cancer among men in the U.S. Compared to Caucasians, Black men have a higher PC incidence, are diagnosed at a younger age, and have a higher PC specific mortality. The reasons for this disparity are multi-faceted and include genetic and socioeconomic factors including access to care. Recent PSA screening guidelines recommend screening in Black men from the age of 40. However, studies suggest uptake of this PSA screening recommendation is very low. Development of a low-cost and rapid screening tool that could be performed in the community could increase PSA testing among Black men. Methods: We developed a total PSA (tPSA) POC lateral flow assay test strip that utilizes immunochromatography to yield different signal intensities based on tPSA concentrations and uses a commercial portable strip reader (Cube) to quantify PSA based on the ratio of signal intensity of test and control line (TC ratio). In an IRB approved study, men undergoing standard PSA testing with a PSA 0.1-20 ng/ml enrolled on protocol after providing informed consent. 50 µL of fingerstick collected blood was mixed with 150 µL of buffer (PBS 1X, 1% BSA, 1% Tween-20) and 100 µL deposited in the chip well and the TC ratio read at 20 min and correlated with a venous blood drawn PSA measured in a CLIA lab. Spearman correlation coefficient was used to assess the correlation between the values of the two tests, and a receiver-operating characteristic curve (ROC) analysis was performed to find the optimal cutoff of TC test to maximize its Sensitivity and Specificity using Youden’s index with a PSA test (dichotomized at 4) as the gold standard. Results: PSA values were plotted against the TC values in a scatter plot from 30 men. The Spearman correlation coefficient between fingerstick and venous PSA was 0.89 (95% CI: 0.78, 0.96). Using a dichotomized approach where a PSA < 4 was Negative, >4 Positive, a ROC analysis demonstrated an AUC of 0.98 (95% confidence interval [CI]: 0.94, 1), with a sensitivity of 85% (95% CI: 62.1% - 96.8%), and specificity of 100% (95% CI: 69.2% - NA). A second cohort of 23 men using a different batch of POC test strips similarly demonstrated an AUC of 0.97 (95% CI: 0.93, 1) with a sensitivity of 86.7% (95% CI: 59.5% - 98.3%), and specificity of 100% (95% CI: 63.1% - NA). Conclusions: Our data show that a PSA POC test is feasible and accurate as a screening test to detect PSA > 4 ng/ml. Patients with positive tests may be referred to the appropriate healthcare provider for further evaluation. PSA POC testing is an alternative and convenient low-cost method to test for elevated PSA in a community setting and improve access to care. This will be further tested by utilizing the device for PSA screening in the community at barbershops.