 The US FDA has approved two Chagas tests , including one approved in April 2010 , and has published guidelines that recommend testing of all donated blood and tissue products . While these tests are not required in US , an estimated 75 – 90 % of the blood supply is currently tested for Chagas , including all units collected by the American Red Cross , which accounts for 40 % of the U.S. blood supply . The Chagas <unk> Network reports current incidents of Chagas @-@ positive blood products in the United States , as reported by <unk> using the screening test approved by the FDA in 2007 . 
