Measurement of prostate-specific antigen by radioimmunoassay

We describe the performance of an RIA for the measurement of prostate-specific antigen (PA). Between-assay precision (CV) for control sera with various analyte concentrations was as follows: mean = 1.67 micrograms/L, CV = 7.1%; mean = 4.47 micrograms/L, CV = 5.6%; mean = 7.15 micrograms/L, CV = 5.5% (n = 19 each). Analytical recovery of PA (nine concentrations ranging from 2.3 to 21.1 micrograms/L) added to a serum pool averaged 101.8% (range 96.1 to 116.1%). Sensitivity (detection limit) of the RIA was 0.25 micrograms/L. Cross reactivity of prostatic acid phosphatase (PAP) in this assay was less than 0.022%. The mean percent B/B0 for 74 specimens from women was 98.9%, not statistically different from that for the zero standard. The normal reference interval for men was 0-2.7 micrograms/L ( 99th percentile), as established by assay of specimens from 276 apparently normal men. Measurement of PA and prostatic acid phosphatase in 205 consecutive serum specimens from patients with clinical evidence of prostate disease similarly placed patients into normal (98) or abnormal groups (54) in 152 cases. However, in 49 cases only the concentration of PA in serum was abnormal. Sequential measurement of both tissue markers in specimens from several patients who were undergoing therapy for prostate cancer appeared to provide supplemental information regarding treatment success.