van der Merwe, PJ, and E Grobbelaar. “Stability of 19-Norandrosterone and 19-Noretiocholanolone Glucuronide in Urine under Various Storage Conditions”. South African Journal of Sports Medicine, vol. 15, no. 2, Dec. 2003, pp. 14-17, doi:10.17159/2078-516X/2003/v15i2a217.