Methods of Calculating Prostate-Specific Antigen Velocity

Abstract

ObjectivesNumerous methods of calculating PSA velocity (PSAV) are used and have the potential to produce differing PSAV results from the same PSA data. We calculated PSAV using three common methods and compared differences between the methods and their predictive value for prostate cancer diagnosis. MethodsFrom a population-based database of PSA results, men with initial PSA<10.0ng/ml and a subsequent diagnosis of prostate cancer or benign histology were identified. Those with ≥3 PSA tests before diagnosis carried out over a minimum of 18 mo were included. PSAV was calculated by using three methods:1.Arithmetic equation of change in PSA over time (AE)2.Linear regression (LR)3.Rate of PSA change using first and last values only (FL)The differences between the methods and test characteristics of each method were compared. ResultsOf the 2204 men included, 716 (32.5%) were diagnosed with prostate cancer and 1488 (67.5%) benign histology. PSAV differed markedly in each method of calculation. The LR and FL methods had similar predictive values, which were higher than the AE method. There was strong agreement for cancer diagnosis between LR and FL (kappa=0.85), with weaker agreement between LR/AE and FL/AE (kappa=0.69 and 0.66, respectively). ConclusionsMethods used to calculate PSAV using the same PSA data can produce markedly different results. Linear regression should be the method of choice for calculating PSAV. Using first and last PSA values only may be adequate for everyday clinical use, as long as measurements are separated by a sufficiently long time period.