Layton JB, Li D, Meier CR, Sharpless JL, Sturmer T, Jick SS, Brookhart MA. Testosterone lab testing and initiation in the United Kingdom and the United States, 2000 to 2011. J Clin Endocrinol Metab. 2014 Mar;99(3):835-42. doi: 10.1210/jc.2013-3570