A 25-year-old man with a thrombus in the superficial femoral vein shows protein C deficiency. Which coagulation factors are most likely inactivated due to this deficiency?

In the context of protein C deficiency and its impact on coagulation factors, the most relevant factors to understand are Factors V and VIII. Protein C is an important plasma protein that, when activated (to activated protein C or APC), plays a key role in regulating coagulation by inactivating specific factors. Specifically, the activated form of protein C preferentially cleaves and thus inactivates Factors V and VIII.

When there is a deficiency of protein C, the regulation of coagulation is impaired, which can lead to an increased risk of thrombosis due to the unregulated activity of factors V and VIII. Factor V is involved in the common pathway of coagulation, facilitating the conversion of prothrombin to thrombin, while Factor VIII acts in the intrinsic pathway, enhancing the formation of thrombin. By inactivating these factors, activated protein C helps to prevent excessive clot formation. Therefore, in the case of a protein C deficiency, the inappropriate activity and presence of both Factors V and VIII contribute significantly to the development of thrombus.

The other factors mentioned in the alternatives do not have the same direct relation to protein C activity, as activated protein C does not inactivate Factors IX, XI, or VII to the same extent or through