Which tube top is used for plasma determinations and contains lithium heparin as an additive?

The green tube top is specifically designed for plasma determinations and contains lithium heparin as an additive. Lithium heparin acts as an anticoagulant, preventing blood from clotting and allowing for the separation of plasma from blood cells during centrifugation. This makes the green top a suitable choice for various laboratory tests that require plasma samples.

In contrast, other options such as the lavender tube contain EDTA, which is primarily used for blood counts and other tests that require whole blood or plasma but involve a different anticoagulation method. The gray tube contains additives like sodium fluoride and potassium oxalate, which are used primarily for glucose testing and not for routine plasma determinations. The red tube is typically used for serum tests and does not contain any anticoagulant, as it is designed for specimens where clotting is required to separate serum from the clot. Therefore, the green tube top is the appropriate choice for the specified use of lithium heparin in plasma determinations.