Anticoagulant-Prothrombin Time – Indications, Procedures, Results

Last updated: February 8, 2026 Medically reviewed by: RxHarun Orthopedic Specialist Doctor Reading time: 3 min read

Anticoagulant-prothrombin time; Clotting time: protime; INR; International normalized ratio

Prothrombin time (PT) is a blood test that measures the time it takes for the liquid portion (plasma) of your blood to clot.

A related blood test is partial thromboplastin time (PTT) .

How the Test is Performed

A blood sample is needed . If you are taking ant blood-thinning medicines, you will be watched for signs of bleeding.

How to Prepare for the Test

Certain medicines can change blood test results.

Your health care provider will tell you if you need to stop taking any medicines before you have this test. This may include aspirin, heparin, antihistamines, and vitamin C.
DO NOT stop or change your medicines without talking to your doctor first.

How the Test will Feel

When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging. Afterward, there may be some throbbing or slight bruising. This soon goes away.

Why the Test is Performed

The most common reason to perform this test is to monitor your levels when you are taking a blood-thinning medicine called warfarin. You are likely taking this medicine to prevent blood clots.

Your provider will check your PT regularly.

You may also need this test to:

Find the cause of abnormal bleeding or bruising
Check how well your liver is working
Look for signs of a blood clotting or bleeding disorder

Normal Results

PT is measured in seconds. Most of the time, results are given as what is called INR (international normalized ratio).

If you are not taking blood thinning medicines, such as warfarin, the normal range for your PT results is:

11 to 13.5 seconds
INR of 0.8 to 1.1

If you are taking warfarin to prevent blood clots, your doctor will most likely choose to keep your INR between 2.0 and 3.0.

Ask your doctor what result is right for you.

Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or test different samples. Talk to your doctor about the meaning of your specific test results

What Abnormal Results Mean

If you are not taking blood thinning medicines, such as warfarin, an INR result above 1.1 means your blood is clotting more slowly than normal. This may be due to:

Bleeding disorders , a group of conditions in which there is a problem with the body’s blood clotting process.
Disorder in which the proteins that control blood clotting become over active ( disseminated intravascular coagulation )
Liver disease
Low level of vitamin K

If you are taking warfarin to prevent clots your doctor will most likely choose to keep your INR between 2.0 and 3.0:

Depending on why you are taking the blood thinner, the desired level may be different.
Even when your INR stays between 2.0 and 3.0, you are more likely to have bleeding problems.
INR results higher than 3.0 may put you at even higher risk for bleeding.
INR results lower than 2.0 may put you at risk for developing a blood clot.

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 medicine
Drinking alcohol
Taking certain over-the-counter (OTC) medicines, vitamins, supplements, cold medicines, antibiotics, or other medicines
Eating food that changes the way the blood-thinning medicine works in your body

Your provider will teach you about taking warfarin (Coumadin) the proper way.

Risks

This test is often done on people who may have bleeding problems. Their risk of bleeding is slightly higher than for people without bleeding problems.

Other slight risks can include:

Fainting or feeling lightheaded
Hematoma (blood accumulating under the skin)
Infection (a slight risk any time the skin is broken)
Multiple punctures to locate veins

Frequently Asked Questions

Is this article a replacement for a doctor?

No. It is educational content only. Patients should consult a qualified clinician for diagnosis and treatment.

When should I seek urgent care?

Seek urgent care for severe symptoms, rapidly worsening condition, breathing difficulty, severe pain, neurological changes, or any emergency warning sign.

References

Add references, clinical guidelines, textbooks, journal articles, or trusted medical sources here. You can edit this area later with a custom field named _rx_references.

Written by Dr. Harun Ar Rashid, MD - Arthritis, Bones, Joints Pain, Trauma, and Internal Medicine Specialist

Dr. Md. Harun Ar Rashid, MPH, MD, PhD, is a highly respected medical specialist celebrated for his exceptional clinical expertise and unwavering commitment to patient care. With advanced qualifications including MPH, MD, and PhD, he integrates cutting-edge research with a compassionate approach to medicine, ensuring that every patient receives personalized and effective treatment. His extensive training and hands-on experience enable him to diagnose complex conditions accurately and develop innovative treatment strategies tailored to individual needs. In addition to his clinical practice, Dr. Harun Ar Rashid is dedicated to medical education and research, writing and inventory creative thinking, innovative idea, critical care managementing make in his community to outreach, often participating in initiatives that promote health awareness and advance medical knowledge. His career is a testament to the high standards represented by his credentials, and he continues to contribute significantly to his field, driving improvements in both patient outcomes and healthcare practices. Born and educated in Bangladesh, Dr. Rashid earned his BPT from the University of Dhaka before pursuing postgraduate training internationally. He completed his MD in Internal Medicine at King’s College London, where he developed a special interest in inflammatory arthritis and metabolic bone disease. He then undertook a PhD in Orthopedic Science at the University of Oxford, conducting pioneering research on cytokine signaling pathways in rheumatoid arthritis. Following his doctoral studies, Dr. Rashid returned to clinical work with a fellowship in interventional pain management at the Rx University School of Medicine, refining his skills in image-guided joint injections and minimally invasive pain-relief techniques.