Milkovic, Borivoj, et al. “Evaluation of Free-to-Total Prostate Specific Antigen (F T PSA), Prostate Specific Antigen Density (PSAD) and (F T) PSAD Sensitivity on Reduction of Unnecessary Prostate Biopsies for Patients With PSA in Gray Zone”. Annali Italiani Di Chirurgia, vol. 85, no. 5, Sept. 2014, pp. 448-53, https://annaliitalianidichirurgia.it/index.php/aic/article/view/2466.