What are the indications for using a green-top tube for blood collection?

The use of a green-top tube for blood collection is particularly indicated for tests that require plasma samples because it contains sodium heparin as an anticoagulant. Sodium heparin works by preventing the clotting process, thus allowing for the collection of plasma, which is the liquid component of blood that contains water, electrolytes, proteins, hormones, and waste products. This makes green-top tubes suitable for various plasma-based tests, especially those requiring rapid processing or where the integrity of coagulation factors must be preserved.

In contrast, other types of tubes, such as red-top tubes, are designed to collect serum, which is the fluid that remains after blood has clotted. Coagulation tests generally require specific additives or no additives at all to measure the clotting ability accurately, making the green-top tube inappropriate for those tests. Additionally, glucose testing typically requires a gray-top tube that contains fluoride to inhibit glycolysis, ensuring the stability of glucose levels during transport and testing.