Which of the following best describes the role of green-top tubes in blood collection?

Green-top tubes are specifically used in blood collection for specimens that require the use of sodium heparin as an anticoagulant. Sodium heparin works by inhibiting thrombin and preventing the formation of blood clots, which is essential for various tests that require the plasma portion of the blood. This type of tube is particularly useful for certain chemistry tests because it allows for the rapid processing of samples while preserving the integrity of the analytes being measured.

The other choices reflect the properties of different types of tubes. For example, sodium citrate is found in blue-top tubes, which are typically used for coagulation testing, while EDTA, an anticoagulant that prevents clotting, is contained in lavender-top tubes primarily used for hematology tests. Serum testing generally involves tubes with no anticoagulant like red-top tubes, which facilitate clotting and serum separation. Thus, sodium heparin in green-top tubes distinctly serves a key role in maintaining the usability of blood samples for specific types of tests in laboratory settings.