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 cont aining similar to 25 mu L of dried whole blood were punched from the f ilter paper and extracted with 500 mu L of buffer. Recovery of PSA was >92%. Imprecision of the filter paper procedure was <10% when corresp onding whole-blood concentrations were >0.35 mu g/L. PSA recovery was unaffected whether blood was applied to the filter paper as one 85-mu L aliquot, two 43-mu L aliquots, or three 28-mu L aliquots. PSA is con tained in the plasma fraction. Variation in hematocrit from 0.61 to 0. 31 caused <+/-10% change in filter paper PSA. Regression analysis show ed: filter paper PSA = 0.86 whole-blood PSA - 0.02; S-y\x = 0.44. Men (153) without prostate cancer gave a 95th percentile of 4.8 mu g/L. PS A in filter paper dried blood was stable for >1 month at -20 to 37 deg rees C and showed no loss of recovery after being mailed to a hot clim ate. We conclude that the filter paper procedure can reliably distingu ish normal from increased concentrations of PSA and that it could faci litate screening to detect occult prostate cancer in large-scale mail- in programs to centralized laboratories.