Prothrombin time (PT) test

Prothrombin time (PT) test is a laboratory-blood test that  measures your blood’s clotting time. Prothrombin is a kind of protein that is produced by liver. In a bleeding condition a serial clotting factors interact and activate one by one to perform clotting. Prothrombin time test shows, how fine this mechanism works and how long the process takes.

Purpose of  prothrombin time test

Finding the cause of bleeding or clotting disorders like;

prothrombin time

  • Abnormal bleeding
  • Easy and abnormal bruising
  • Nosebleedings
  • Bleeding gums
  • Blood clot in a vein or artery
  • Heavy and longer menstrual periods
  • Determining liver disease
  • Detecting any bleeding disorder before surgery
  • Checking the effects of a blood thinning medicine; warfarin (coumadine) that is used to prevent blood clots

How the prothrombin test is done ?

You can check your prothrombin time by 2 ways. You can give a tube of blood in a medical laboratory. Your blood is collected in a anticoagulant containing laboratory test tube. You can measure you PT yourself  by  using a device that looks like glucometer in your home. Please ask your doctor to use or stop taking your medicines before prothrombin time test, don’t pause or stop taking your medicines without asking your doctor.

Prothrombin time (PT) normal values

Prothrombin time normal range may change according to the laboratory, analyser and reagents-chemicals. Laboratory’s PT normal range should be known to evaluate the results as prothrombin time.

This test results may be evaluated by 2 ways

1- PT result as seconds: Its average value is between 10-14 seconds. Longer values than 14 means your blood needs more time for clotting or shorter values means the clotting time is short for your blood.

Prothrombin Time (PT) Normal Value: 11-14 seconds

2- PT result as INR: INR means “international normalized ratio” and that is used to eliminate the differences between laboratories and test methods. With INR value your result won’t be changed  anywhere in world so evaluation of your result will be same.

INR normal range:                  0,8-1,1

INR range for warfarin users: 2-3

Evaluation of prothrombin ime results

1-  Longer PT results

Longer results of  PT means your blood is clotting more slowly than normal. This could be caused by;

  • Liver disease
  • Anticoagulant medicine usage
  • Bleeding disorders;
  • Blood clotting factor’s deficiency (factors I, II, V, VII, or X)
  • Hereditary factor deficiency
  • Vitamin K deficiency, low level of vitamin K

2- Shorter PT results

Shorter values  of  PT means your blood is  clotting  faster and may be caused by some factors like;

  • Eating so many vitamin K containing food; broccoli, chickpeas, turnip greens, kale, soybean products, green tea, liver.
  • Birth control pills
  • Estrogen hormone treatment


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