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The PLCO trial routinely measured total prostate-specific antigen (PSA) levels for approximately 38,000 males in the intervention arm as part of the screening protocol. Free PSA (fPSA) levels were not collected in the trial. This sub-study was an effort to go back and measure PSA and fPSA levels in the original blood samples for ~6,800 participants. The percent free PSA (%PSA) was calculated and compared among demographic and clinical parameters.


The study cohort includes males in the intervention arm with an adequate PSA screen, baseline questionnaire and known race. An initial effort randomly selected participants who were eligible and randomized by February 1996. To maximize the minority participation, a second, subsequent selection was made in which all eligible nonwhite and Hispanic men that were randomized by July 1997 were included. As a result 47% of ~10,400 eligible white and 92% of the eligible non-white or Hispanic men were selected.


  • The trial, which started in 1993, only began recruiting participants aged 55-59 in early 1996. Therefore, since white participants were only selected in the first effort there are very few whites in this data set aged 55-59.
  • The original study and main findings (Urology, 2001; see below) include participants from Brooklyn that are not available in this data set.
  • Only blood samples from the baseline screening round (T0) were used in the main findings analysis; however, ~50 blood samples from other study years are included in this data set.

Data Collected

ImmunoRadioMetric Hybritech PSA and Hybritech free PSA assays from Beckman Coulter were used to determine the value of PSA and fPSA in accordance with the procedures specified by the manufacturer. The %fPSA was calculated by dividing the value for fPSA by the value for PSA from the same serum sample. The Hybritech assay for PSA is not accurate at less than 0.1 ng/mL; as such, %fPSA is not included when the fPSA level is 0.05 ng/mL or less or the PSA level is 0.2 ng/ml or less.

Free PSA data can be obtained in the Free PSA dataset.

Summary Available Data
  • ~6800 participants
    • ~4800 white non-hispanic
    • ~2000 other
  • Median % fPSA: 19% (IQR: 14-26%)
  • Free PSA
  • Total PSA
  • Percent Free PSA

Main Findings