Around 8% of adults in the U.S. have undiagnosed hypertension.
Roger, Veronique L., Alan S. Go, Donald M. Lloyd-Jones, Emelia J. Benjamin, Jarret D. Berry, et al.; on behalf of the American Heart Association Statistics Committee and Stroke Statistics Subcommittee. Heart Disease and Stroke Statistics–2012 Update. Circulation. 2012; 125: e2-e220. http://circ.ahajournals.org/content/125/1/e2