What is the additive in dark green top tubes commonly used for blood collection?

The correct choice identifies sodium heparin as the additive found in dark green top tubes used for blood collection. Sodium heparin is an anticoagulant that prevents blood from clotting by inhibiting thrombin and factor Xa, both of which are crucial components of the coagulation cascade. This makes dark green top tubes particularly valuable in situations where plasma is needed for a variety of laboratory tests, such as chemistry panels.

In contrast, sodium citrate, which is the additive in light blue top tubes, is used primarily for coagulation studies, as it binds calcium ions and works differently than heparin. EDTA, found in lavender top tubes, also acts as an anticoagulant but achieves this through a different mechanism, chelating calcium ions and preventing clot formation. Potassium EDTA, while similar to EDTA, is often used in specific contexts such as blood banking, so it is not found in dark green top tubes. Thus, the specification of sodium heparin for dark green tubes is accurate and crucial for understanding the purpose of different tube colors and their respective additives in blood collection.