Phlebotomy Technician Practice Exam (NCPT/CPT)

The color of the tube cap/top is important for proper blood sample collection and testing, as different additives are used in different colored tubes. The presence of sodium fluoride oxalate, used to prevent blood from clotting, is indicated by a grey cap/top. Red tubes usually contain clot activators, blue tubes contain anticoagulants like citrate, green tubes are typically used for heparin and EDTA, and grey tubes are commonly used for fluoride oxalate. Therefore, the other options (red, blue, green) are incorrect as they have different additives present.