Lab test
Prothrombin Test: Prothrombin Time PT with INR
The prothrombin time test measures how long blood takes to clot through the extrinsic and common clotting pathways, and the result is usually reported with the International Normalized Ratio (INR) so it can be compared across laboratories.
- Typical price
- From $29
- Results
- 1-3 business days
- Preparation
- See preparation notes below
- Sample
- Blood draw or sample collection at a local center
About this test
The prothrombin time test measures how long blood takes to clot through the extrinsic and common clotting pathways, and the result is usually reported with the International Normalized Ratio (INR) so it can be compared across laboratories. The activated partial thromboplastin time (aPTT) may be included to assess the intrinsic pathway. Together these tests evaluate clotting function, help monitor anticoagulant therapy such as warfarin, and investigate unexplained bleeding or clotting.
What this test measures
- Prothrombin Time (PT) Measures the time in seconds for blood to clot via the extrinsic and common pathways.
- International Normalized Ratio (INR) A standardized ratio derived from PT that allows comparison across laboratories, especially for warfarin monitoring.
- Activated Partial Thromboplastin Time (aPTT) Measures the intrinsic and common pathways when included in the panel.
Who this test may be right for
- People taking warfarin or similar anticoagulants being monitored
- Individuals with unexplained bleeding or bruising
- Patients with suspected clotting disorders
- People with liver disease affecting clotting factor production
- Patients being assessed before surgery or procedures
Before your visit
- Report all anticoagulant and other medications, especially warfarin
- Avoid alcohol excess and major dietary changes before testing unless advised
- No fasting is usually required
- Collect at the time recommended for therapy monitoring
Understanding your results
A prolonged PT or high INR can indicate a bleeding tendency or the effect of anticoagulant therapy, while a short PT is less commonly significant. The aPTT helps localize clotting problems to different pathways. Results are interpreted with your medications, liver function, and clinical situation. Discuss your PT, INR, and aPTT results and any changes to therapy with a healthcare provider.
Order this test online
- Buy online in a few minutes - no doctor's visit needed for most tests.
- Sample collection at a patient service center near you.
- Results are typically ready within 1-3 business days.
- Secure, lab-reviewed results delivered to your account.
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Questions people ask
What is the INR used for?
The INR standardizes the prothrombin time so results from different laboratories can be compared. It is especially important for monitoring warfarin therapy.
Do I need to fast for a PT or INR test?
Fasting is usually not required, although some panels request it. Follow the instructions included with your order.
What does a prolonged PT mean?
A prolonged prothrombin time can reflect a clotting factor deficiency, liver disease, or the effect of an anticoagulant. Discuss the meaning with a healthcare provider.
Does this panel check warfarin and heparin?
PT and INR are mainly used to monitor warfarin, while the aPTT is often used to assess heparin. The specific tests included depend on the panel ordered.
What does the Prothrombin Test: Prothrombin Time PT with INR measure?
This test measures blood clotting factors by determining the following: activated partial thromboplastin time; INR; and prothrombin time (PT).
Do I need to fast before this test?
Follow the lab's instructions.
How long do results take?
Most Prothrombin Test: Prothrombin Time PT with INR results are released in 1-3 business days. Specialty testing can take longer.
Is this test right for me?
This page is educational and not medical advice. Talk to a licensed healthcare provider about which tests fit your situation.
LabBookings is an independent directory. We compare test details and pricing information, but we are not a laboratory and we do not perform testing or provide medical advice. Always talk to a licensed healthcare provider about your results and treatment.
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