Prostate-specific antigen variability in men without prostate cancer: effect of sampling interval on prostate-specific antigen velocity.

OBJECTIVES: To evaluate short-term and long-term variability between prostate-specific antigen (PSA) measurements to determine the most appropriate PSA sampling interval and rate of PSA change (PSA velocity) to distinguish between men with and without prostate cancer.
METHODS: Retrospective study of PSA variability and PSA velocity in three groups of men without a diagnosis of prostate cancer and PSA levels less than 10 ng/mL: 56 men with a histologic diagnosis of benign prostatic hyperplasia (BPH; histologic BPH group) and 527 men with no history of cancer (noncancer group) who were part of the Baltimore Longitudinal Study of Aging and had PSA sampled at 2-year intervals (long-term), and 223 men with a clinical diagnosis of BPH (clinical BPH group) who had PSA sampled at 3-month intervals (short-term). PSA variability (deviation between consecutive measurements) and PSA velocity based on both two consecutive measurements and three consecutive measurements (average velocity) were calculated for each study group.
RESULTS: PSA velocity is the deviation in PSA measurements relative to the elapsed time between the measurements. Because the variability in PSA between measurements was similar for the groups, the major factors that influenced PSA velocity were the sampling interval between PSA measurements, and to a lesser extent, the number of repeat PSA measurements. The 99th percentile for PSA velocity was 0.7 (histologic BPH group) and 0.75 ng/mL per year for the noncancer group when three measurements with a 24-month PSA sampling interval were used. However, the 99th percentile for PSA velocity was 5.8 and 2.4 ng/mL per year when three measurements with 3-month and 6-month PSA sampling intervals were used. Using three measurements, the percentage of subjects with a PSA velocity more than 0.75 ng/mL per year was 1% for the groups with a 24-month PSA sampling interval and 28% and 17% for 3-month and 6-month PSA sampling intervals, respectively. The 99th percentile for PSA velocity and the percentage of subjects with a PSA velocity more than 0.75 ng/mL per year was higher using two measurements compared to three measurements regardless of PSA sampling interval.
CONCLUSIONS: PSA velocity is inversely related to the interval between PSA measurements. A PSA velocity more than 0.75 ng/mL per year is useful in distinguishing between men with and without prostate cancer when: (1) velocity is based on three consecutive measurements; and (2) PSA is sampled long-term (2 years) but not short-term (3 to 6 months).