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Prothrombin time (PT) - Results

Alternative Names

PT; Pro-time; Anticoagulant-prothrombin time

Normal Values:

The normal range for someone who is not taking a blood thinner medication is 11 - 13.5 seconds.

The PT result will be longer in persons who take blood thinners. Ask your doctor what result is right for you.

Note: Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.

The examples above show the common measurements for results for these tests. Some laboratories use different measurements or may test different specimens.

What abnormal results mean:

When any of the blood clotting factors are lacking or not working properly, the PT is prolonged.

A PT result that is too high or too low in someone who is taking warfarin (Coumadin) may be due to:

The wrong dose of medication
Drinking alcohol
Taking certain over-the-counter medicines, vitamins, supplements, cold medicines, antibiotics, or other drugs
Eating a food that changes the way the blood thinning medication works in your body

Increased PT may also be due to:

Bile duct obstruction
Disseminated intravascular coagulation
Liver disease
Malabsorption
Vitamin K deficiency
Factor VII deficiency
Factor X deficiency
Factor II (prothrombin) deficiency
Factor V deficiency
Factor I (fibrinogen) deficiency

Reviewed last on: 2/13/2011
David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.

References

Schafer AI. Approach to the patient with bleeding and thrombosis. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 178.

Schmaier AH. Laboratory evaluation of hemostatic and thrombotic disorders. In: Hoffman R, Benz EJ Jr, Shattil SJ, et al, eds. Hoffman Hematology: Basic Principles and Practice. 5th ed. Philadelphia, Pa: Churchill Livingstone Elsevier; 2008:chap 122.

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