Assay of prostate-specific antigen from whole blood spotted on filter paper and application to prostate cancer screening.

We report the measure of prostate-specific antigen (PSA) from extracts of blood dried on filter paper. Five 3-mm (diameter) paper discs containing approximately 25 microL of dried whole blood were punched from the filter paper and extracted with 500 microL of buffer. Recovery of PSA was > 92%. Imprecision of the filter paper procedure was <10% when corresponding whole-blood concentrations were >0.35 micrograms/L. PSA recovery was unaffected whether blood was applied to the filter as one 85-microL aliquots, two 43-microL aliquots, or three 28-microL aliquots. PSA is contained in the plasma fraction. Variation in hematocrit from 0.61 to 0.31 caused <+/-10% change in filter paper PSA. Regression analysis showed: filter paper PSA = 0.86 whole-blood PSA - 0.02; Sy/x = 0.44. Men (153) without prostate cancer gave a 95th percentile of 4.8 micrograms /L. PSA in filter paper dried blood was stable for >1 month at -20 to 37 degrees C and showed no loss of recovery after being mailed to a hot climate. We conclude that the filter paper procedure can reliably distinguish normal from increased concentrations of PSA and that it could facilitate screening to detect occult prostate cancer in large-scale mail-in programs to centralized laboratories.