Retrospective specimens from repositories or specimens purchased from commercial vendors were also included in the study. In addition to the Geenius HIV 1/2 Supplemental Assay, the GS HIV 1/HIV 2 PLUS O EIA, Bio-Rad HIV-1 Western blot, and the Bio-Rad Multispot HIV 1/HIV-2 Rapid Test were utilized as reference methods. Historical data, when available, was also used. All samples were identified with a unique study number and included the following populations/panels: