Prostate specific antigen doubling time calculation: not as easy as 1, 2, 4

PURPOSE: Although prostate specific antigen doubling time is widely used to predict outcomes such as time to progression and prostate cancer specific mortality, clinicians may be unaware of the impact of method on prostate specific antigen doubling time calculation. We present a critical review of the literature to assess the diversity of methods used to calculate prostate specific antigen doubling time. We then describe the need for methodological consistency with the literature by showing examples from our clinical experience at our institution. MATERIALS AND METHODS: A comprehensive review of articles evaluating prostate specific antigen doubling time as a prognostic and predictive indicator in various prostate cancer disease states was performed using PubMed. Case examples were drawn from the prostate cancer database at our institution. The database is a registry of 4,651 patients with prostate cancer who have been seen at our institution since 1998. RESULTS: The methodology of prostate specific antigen doubling time calculation is inconsistent in the literature. Based on our experience and data presented in the literature the different methods in the literature are not always interchangeable. Small deviations from the methods outlined in a study can sometimes lead to wide variation in calculated prostate specific antigen doubling time. This variation of up to several months or longer is large enough to cause errors in assessment of prognosis and can even lead to incorrect management. The rules for prostate specific antigen doubling time calculation found in the literature can be categorized into 4 parameter groups, including method, calculation interval, data acquisition rules and data analysis rules. Case examples illustrate the importance of adherence to the literature with regard to each parameter. CONCLUSIONS: Consistency with the literature in methodological elements of prostate specific antigen doubling time calculation is essential for the accurate calculation of prostate specific antigen doubling time. Clinicians and researchers should understand how methodological differences influence the value of calculated prostate specific antigen doubling time for purposes of patient care and research.