Prothrombin Test
Prothrombin Test is a laboratory test you can order directly. The prothrombin test measures how long it takes your blood to clot. It is often ordered to check for bleeding disorders, monitor blood-thinning medications, or assess liver function.
- Sample type
- blood
- Category
- Coagulation
- Turnaround
- 1-3 business days
- Price
- $29
- Referral
- Not required
The prothrombin test measures how long it takes your blood to clot. It is often ordered to check for bleeding disorders, monitor blood-thinning medications, or assess liver function.
What it measures
- Prothrombin Time (PT) — The time in seconds for a clot to form.
- International Normalized Ratio (INR) — A standardized ratio that allows comparison across labs.
- Prothrombin Activity — A percentage showing how well your clotting factors work.
- Fibrinogen — A protein that helps form clots; sometimes measured with PT.
Who it is for
A doctor may order this test if you have unexplained bleeding or bruising, or if you take warfarin or another blood thinner. It is also used before surgery or to monitor liver disease.
Preparation
No fasting is needed for a prothrombin test. Tell your doctor about all medications, especially blood thinners, as they can affect results.
Results and what they mean
Results are reported as seconds for PT and as a number for INR, along with a reference range. Your clinician interprets these values based on your health and medications. This is general information, not medical advice; discuss your results with a healthcare professional.
How to order this test
- Choose the test and place a confidential order online.
- Select a certified collection site and pick a time that suits you.
- Have your specimen collected — most draws take only a few minutes.
- Review results in a secure portal, typically within 1–3 days.
Preparation, hours, and pricing vary by site; confirm details directly with the lab before your visit.
Availability by state
Direct-access online ordering for the prothrombin test is available in most states. It is currently unavailable in 6 states:
Everywhere else you can order confidentially and collect your sample at a certified site. Browse by state →
Frequently asked questions
Does a prothrombin test hurt?
It is a standard blood draw from a vein in your arm. You may feel a brief pinch or sting.
How long does it take to get results?
Typically 1 to 3 business days, though it may be faster in urgent situations.
Can I eat or drink before the test?
Yes, you can eat and drink normally unless your doctor gives other instructions.
What if my INR is too high or too low?
Your doctor will review your results and may adjust medication or order further tests. Do not change any medication without talking to your doctor.