Prothrombin time (PT)

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PT; Pro-time; Anticoagulant-prothrombin time

The normal range for someone who is not taking a blood thinner medication is 11 to 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.

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:

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• 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

Review Date: 02/13/2011
Reviewed By: 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.

A.D.A.M., Inc. is accredited by URAC, also known as the American Accreditation HealthCare Commission (www.urac.org).