A, Diagnosis of clinical severity (mild, moderate, severe) of hemophilia is based on in vitro coagulant activity as shown. B, Distribution of severe and moderately severe disease in hemophilia A and hemophilia B. Data based on a survey of hemophilia treaters in the United States in the early 1970s and included 20,297 patients with hemophilia A and 5202 patients with hemophilia B. Estimates were made from the number of patients requiring blood products during the year prior to survey: Patients with mild disease were excluded. (From Department of Health and Human Services, 1972 285 ). Source: Hemophilia B: Factor IX Deficiency, The Online Metabolic and Molecular Bases of Inherited Disease Citation: Valle D, Beaudet AL, Vogelstein B, Kinzler KW, Antonarakis SE, Ballabio A, Gibson K, Mitchell G. The Online Metabolic and Molecular Bases of Inherited Disease; 2014 Available at: http://ommbid.mhmedical.com/DownloadImage.aspx?image=/data/books/971/ch173fg2.png&sec=62650300&BookID=971&ChapterSecID=62650290&imagename= Accessed: October 08, 2017 Copyright © 2017 McGraw-Hill Education. All rights reserved