Chagas disease is caused by the parasite Trypanosoma cruzi and is spread by infected insects known as triatomine bugs. The parasite is endemic in Central and South America. In the United States, blood donors are screened once for antibodies to T. cruzi because the risk of acquiring Chagas disease from the bite of an infected triatomine bug is considered low.

Confirmation of infection requires a reactive screening test result followed by a positive supplemental test. Under current FDA guidance, donors whose supplemental test results are positive or ambiguous are permanently deferred from blood donation, with no option for reentry.

The American Red Cross is conducting a study of blood donors who receive ambiguous T. cruzi supplemental test results during routine screening. Donors who participate in the study will complete a brief questionnaire to help identify potential risk factors for T. cruzi exposure and will provide a blood sample for additional testing.

The outcome of the study will help to better understand what ambiguous test results mean for blood donors and support evidence-based evaluation of current FDA guidance.