Ayatollahi, Hossein, et al. “Ratios of Free to Total Prostate-Specific Antigen and Total Prostate Specific Antigen to Protein Concentrations in Saliva and Serum of Healthy Men”. Urology Journal, vol. 4, no. 4, Feb. 2009, pp. 238-41, doi:10.22037/uj.v4i4.105.