A　sequential　design　is　proposed　to　test　whether　the　accuracy　of　a　binary　diagnostic　biomarker　meets　the　minimal　level　of　acceptance.　The　accuracy　of　a　binary　diagnostic　biomarker　is　a　linear　combination　of　the　marker＇s　sensitivity　and　specificity.　The　objective　of　the　sequential　method　is　to　minimize　the　maximum　expected　sample　size　under　the　null　hypothesis　that　the　marker＇s　accuracy　is　below　the　minimal　level　of　acceptance.　The　exact　results　of　two-stage　designs　based　on　Youden＇s　index　and　efficiency　indicate　that　the　maximum　expected　sample　sizes　are　smaller　than　the　sample　sizes　of　the　fixed　designs.　Exact　methods　are　also　developed　for　estimation,　confidence　interval　and　p-value　concerning　the　proposed　accuracy　index　upon　termination　of　the　sequential　testing.　Published　2016.　This　article　is　a　U.S.　Government　work　and　is　in　the　public　domain　in　the　USA.