What additive is found in a light blue top tube?

The correct answer is sodium citrate, which is the additive found in a light blue top tube. This particular additive acts as an anticoagulant, preventing blood from clotting during the testing process. Sodium citrate works by binding calcium ions in the blood, which is a critical component necessary for the clotting cascade to occur.

This is particularly important for tests that require whole blood or plasma, as it preserves the sample's integrity by ensuring that it remains in its liquid form. Tests commonly associated with light blue top tubes include prothrombin time (PT) and activated partial thromboplastin time (aPTT), both of which are essential for assessing coagulation status.

The other options do not apply here. Lithium heparin is found in green top tubes and is another anticoagulant but functions differently than sodium citrate. Silica is an additive used in serum separation tubes, not in light blue top tubes. "None" would indicate that there is no additive present, which contradicts the known composition of the tube. Thus, sodium citrate is indeed the correct and appropriate answer for a light blue top tube.