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

Abstract

We report the measure of prostate-specific antigen (PSA) from extracts of blood dried on filter paper. Five 3-mm (diameter) paper discs containing ~25 μL of dried whole blood were punched from the filter paper and extracted with 500 μL of buffer. Recovery of PSA was >92%. Imprecision of the filter paper procedure was <10% when corresponding whole-blood concentrations were >0.35 μg/L. PSA recovery was unaffected whether blood was applied to the filter paper as one 85-μL aliquot, two 43-μL aliquots, or three 28-μL aliquots. PSA is contained in the plasma fraction. Variation in hematocrit from 0.61 to 0.31 caused 1 month at -20 to 37 °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.