What is the additive in a green top tube?

The additive in a green top tube is sodium heparin, which serves as an anticoagulant to prevent blood from clotting during the collection and storage process. Sodium heparin works by inhibiting thrombin and factor Xa, which are critical components of the coagulation cascade. This allows for the collection of whole blood or plasma without clot formation, making the green top tube suitable for various tests, particularly those requiring plasma analysis.

Other additives mentioned, such as potassium EDTA, are found in lavender top tubes and act as chelating agents that bind calcium to prevent clotting in different types of tests. Calcium carbonate is not typically used as an additive in blood collection tubes, while lithium heparin is associated with a different color tube (usually grey), which serves a different purpose or specific tests.