What type of blood test would require a green-topped tube?

The green-topped tube is specifically designed to contain sodium heparin, which is an anticoagulant. This type of tube is primarily used for collecting blood specimens for tests that require plasma, such as serum chemistry tests.

In serum chemistry tests, the sample must be free from clotting factors, and heparin effectively prevents clot formation while preserving the integrity of the plasma. This is especially important for glucose tests, which are also performed in green-topped tubes, but the broader category of serum chemistry tests encompasses a wider range of analyses that are typically performed on plasma samples.

Thus, when considering the context of the question—identifying the appropriate test that utilizes a green-topped tube—serum chemistry tests best fits the criteria, as they routinely involve analyzing a variety of substances within the plasma.