Thrombophlebitis is characterized by which of the following?

Thrombophlebitis is a medical condition characterized specifically by the inflammation of a vein that occurs in conjunction with the formation of a thrombus, or blood clot, within that vein. This condition typically arises in the superficial veins of the legs and can lead to various symptoms, such as pain, redness, and swelling in the affected area. The inflammation is often caused by irritation or a response to the thrombus itself, making option C the correct choice for this question.

Other options do not accurately reflect the definition of thrombophlebitis. Inflammation of the arteries pertains to a completely different condition, while the formation of a thrombus in the heart refers to a cardiac issue that does not involve vein inflammation. Finally, while fibrinogen levels can be higher in various clotting disorders, they are not a defining characteristic of thrombophlebitis itself, thus making option C the most precise choice.