Which medication has been shown to interfere with in vivo Tc99 labeling of RBC?

Heparin is known to interfere with in vivo labeling of red blood cells (RBCs) using technetium-99m (Tc-99m). This interference occurs because heparin can affect the coagulation process and alter the binding of technetium to red blood cells during the labeling process. The mechanism behind this interaction is rooted in heparin's anticoagulant properties, which can disrupt normal cellular function and the ability of the red blood cells to properly incorporate the radioactive tracer.

On the other hand, other medications listed, such as warfarin, aspirin, and clopidogrel, primarily act as anticoagulants or antiplatelet agents, but they do not have the same direct effect on the labeling process as heparin does. Warfarin affects vitamin K-dependent clotting factors and may prolong bleeding times, while aspirin and clopidogrel inhibit platelet aggregation. However, these medications do not directly interfere with the in vivo labeling of Tc-99m to red blood cells in the same way that heparin does. Therefore, the unique impact of heparin on the labeling process makes it the correct choice regarding its interference with in vivo Tc-99m labeling of RBCs.