What is the primary function of lithium in the light green top tube?

Lithium in the light green top tube primarily functions to inhibit thrombin, which is a crucial component of the blood coagulation process. This action is particularly essential when drawing blood for plasma testing, as inhibiting thrombin prevents the formation of clots in the sample. As a result, it ensures that the serum or plasma remains in a liquid state, allowing accurate analysis of various blood components, including electrolytes and certain chemicals.

The light green top tube contains lithium heparin as an anticoagulant, and its capability to inhibit thrombin makes it useful for specific laboratory tests that require an unclotted sample. This distinguishes it from other options, such as glucose preservation or testing for heavy metals, which are not the primary roles of lithium in this context. Similarly, while some tubes are designed to facilitate coagulation, the function of the light green top tube specifically emphasizes anticoagulation through the action of lithium. This specialized function is critical in ensuring that laboratory results are reliable and informative for patient care.