A method and a blood oxygen tester for determining whether a blood sample is arterial or venous blood are disclosed. A blood oxygen tester for determining whether a blood sample is arterial or venous blood includes a housing and a blood sample receptacle defined by the housing. A blood oxygen sensor is in communication with the blood sample receptacle and a test result indicator is in communication with the blood oxygen sensor. The indicator is responsive to the blood oxygen sensor for indicating whether a tested blood sample is arterial blood or venous blood.
