QS Study

Prothrombin time (PT)

The time required for coagulation to take place is known as Prothrombin time. It is a blood test that measures the time it takes for the liquid portion (plasma) of your blood to clot. An abnormal prothrombin time is often caused by liver disease or injury or by treatment with blood thinners.

Normal value: About 12 seconds. A normal PT indicates that a normal amount of blood-clotting protein is available. A high PT usually means that there is serious liver damage or cirrhosis.

Fig: Prothrombin time

The prothrombin time is made longer by:

  • Blood-thinning medicine, such as warfarin.
  • Low levels of blood clotting factors.
  • The absence of any of the clotting factors.
  • An increase in the use of the clotting factors.

If your blood doesn’t clot in the normal amount of time, you may:

  • be on the wrong dose of warfarin
  • have liver disease
  • have vitamin K deficiency
  • have a bleeding disorder, such as factor II deficiency

Importance: Give indication about the clotting factors in body. A prothrombin time test can be used to check for bleeding problems. PT is also used to check whether medicine to prevent blood clots is working.