Final answer:
The abbreviation for the test measuring the clotting time of plasma proteins, specifically prothrombin, is PT or Prothrombin Time.
Step-by-step explanation:
The abbreviation for the test measuring the clotting time of plasma proteins, specifically prothrombin, is PT. PT stands for Prothrombin Time, which evaluates the activity of the common pathway, the final coagulation pathway that leads to the formation of a blood clot. It is commonly used to monitor the effectiveness of anticoagulant therapy such as warfarin.