Prothrombin Time INR (PT/INR) Test

The PT/INR test is a simple blood test that shows how long it takes your blood to clot. Your body relies on proteins called "clotting factors" to stop bleeding when you are injured. The PT/INR test checks whether these clotting factors are working properly.  It is commonly used to evaluate how well your blood is clotting  and to monitor certain medications, such as blood thinners, that can affect clotting time. A healthcare provider may recommend this test if you have symptoms or are in a situation where understanding how your blood is clotting is important. PT/INR may be used along with other tests to fully evaluate blood clotting.

Normal prothrombin time often falls around 9–12 seconds, though ranges can vary slightly by lab.¹ This is why the INR is used to standardize results.

A higher prothrombin time (PT) means your blood is taking longer than usual to form a clot. This can sometimes show up as symptoms like easy bruising, bleeding that lasts longer from small cuts, or more frequent nosebleeds. PT can be affected by several factors, including certain medications, vitamin K intake from food, and how your body is processing clotting proteins.² That’s why PT results are typically looked at alongside INR, which helps standardize the numbers and give a clearer picture of overall clotting time.

No. The PT/INR test does not predict whether you currently have a blood clot. Instead, it measures how long it takes your blood to clot, offering insight into overall clotting time rather than spotting an active clot.
 

If you notice blood clot symptoms such as³:
 

• Swelling, warmth, or pain in one leg or arm
• Skin that appears red, blue, or unusually discolored
• Sudden shortness of breath or chest pain

Seek immediate medical care, as these symptoms may indicate a medical emergency.

Multiple factors can impact the results of a PT/INR blood test. Some of these include:
 

• Vitamin K intake: Foods like leafy greens (spinach, kale, broccoli) can affect clotting. 
• Medications and supplements: Some prescriptions, over-the-counter medicines (like ibuprofen or aspirin), and herbal products can affect your results.
• Alcohol use: Alcohol can affect how your body processes clotting factors and medications.
• Illness: Being sick—such as with a fever, infection, vomiting, or diarrhea—may impact your results.
• Liver health: Conditions affecting the liver can change clotting factor production.
• Medication adherence: If you are prescribed blood thinners, taking them inconsistently can impact results.

Your testing will be performed in a CLIA-certified clinical laboratory. Labcorp provides leading-edge medical laboratory tests and services through a national network of primary clinical laboratories and specialty testing laboratories. Our labs perform regular quality assurance testing to ensure our results are accurate.

Your results will be provided to you through our secure online portal to view or print. Results are also made available through a secure portal to the independent healthcare provider who placed your test order.  If you are accessing your results through your Labcorp Patient™ account, all users linked to the account will have access to all OnDemand test results. Results may also be provided to a local, state, and/or federal health authority; for example, many states require the testing laboratory and physician to report test results for certain communicable diseases, such as COVID-19, to local or state health departments.  

If you have questions or comments regarding the Labcorp Notice of Privacy Practices, or have a complaint about our use or disclosure of your PHI or our privacy practices, please contact: privacyofficer@labcorp.com, call us at (877) 234-4722 (877-23-HIPAA) and ask for the Labcorp HIPAA Privacy Officer, or send a written request to: HIPAA Privacy Officer, Labcorp, 531 South Spring Street, Burlington, NC 27215. You also may file a complaint with the Secretary of the U.S. Department of Health and Human Services.

Visit the Labcorp OnDemand® website to browse and purchase laboratory tests and create your Labcorp Patient™ account to view your results. All Labcorp OnDemand testing requires an order from an authorized healthcare professional. For your convenience, Labcorp OnDemand has contracted with independent professional entities (collectively, Providers) to deliver healthcare provider services. Visit a Labcorp location for sample collection; or, if using an at-home collection kit, collect your sample yourself. We’ll let you know when your results are ready and can be accessed through your Labcorp Patient™ account.

To align with clinical best practices, we’ve set an age maximum of 100 for consumer-initiated testing. This limit was set to encourage individuals in more advanced age groups - who may have complex medical needs - to receive personalized guidance about testing from their healthcare providers.