Prostate‐specific antigen assay using whole blood samples spotted on filter paper and its application to mass screening for prostate cancer

Aim:  The disc assay system for prostate‐specific antigen (PSA) is a novel technique using a small amount of whole blood on filter paper. The accuracy of this assay system and its feasibility for use in prostate cancer mass screening were evaluated.Methods:  In the first arm of the study, to evaluate the accuracy of the disc assay system, PSA values were determined by both a disc assay system and a standard serum assay system using the same blood samples obtained from 420 outpatients. In the second arm of the study, the feasibility and reliability of the disc assay system were examined in prostate cancer mass screening. A total of 2475 men were screened by the disc assay (disc group) and 3348 men were screened by the standard serum assay (serum group) in the first step of mass screening. In the second step of the screening in the disc group, 101 men underwent PSA tests by a standard serum assay, then the first PSA values determined by the disc assay were compared with the second PSA values determined by the standard serum assay. In the second step of the screening in the serum group, 94 men underwent additional PSA tests by a serum assay, and then the first PSA values were compared with the second PSA values. Two men in each group were excluded from analysis because the true PSA values of the first step were not available (more than 50 ng/mL).Results:  The PSA values determined by the disc assay closely correlated with those obtained by the standard assay (r = 0.987) in 295 outpatients with PSA levels between 1.0 and 20 ng/mL. In the PSA mass screening, the PSA values determined in the first step closely correlated with those in the second step both in the disc group (r = 0.916) and in the serum group (r = 0.845). A significant dissociation of the two PSA values was observed in seven of 99 men in the disc group and in three of 92 men in the serum group. However, there was no statistical significance in the incidence of dissociation in the two PSA values between the disc group and the serum group.Conclusions:  The disc assay system seems to be a sensitive and accurate assay system. The feasibility and reliability of the disc assay system were well demonstrated in the field during prostate cancer mass screening.