PT blood test
Prothrombin time
In short
A typical adult PT result is 11 to 13.5 seconds (varies by lab). A PT above the range can mean the blood is clotting a bit more slowly. How far above, the INR, and any blood thinner taken matter more than the seconds alone. Always read your result against the range printed on your own report.
How many seconds a blood sample takes to form a clot.
The lab adds a clotting trigger to the sample and times how long a clot takes to form. This checks clotting proteins made by the liver, several of which need vitamin K to work. The seconds differ from lab to lab more than most tests, so the INR puts them on one shared scale.
Is my PT high or low?
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Typical range
| For | Range | Unit |
|---|---|---|
| Adults · varies by lab | 11–13.5 | seconds |
Typical ranges for adults. Labs differ a little, so the range printed next to your result is the one to go by.
If your PT is high
A PT above the range can mean the blood is clotting a bit more slowly. How far above, the INR, and any blood thinner taken matter more than the seconds alone.
Common reasons
- Taking a blood thinner, especially the kind that blocks vitamin K
- A sample tube not filled fully, or a delay before testing
- Low vitamin K, from a poor diet, some antibiotics or poor absorption
- Less often: liver disease, since the liver makes most clotting proteins
- Less often: an inherited low level of one clotting protein
- Less often: DIC, a serious illness in which clotting proteins get used up
If your PT is low
A PT a little below the range is rarely a concern. It most often reflects the lab's method or how the sample was handled.
Common reasons
- Natural variation between people and between lab methods
- How the sample was drawn, stored or handled
- Pregnancy, or hormone medicines such as birth control pills
What can throw it off
An under-filled sample tube or a delay before testing can make the PT read longer than it really is.
Questions to take to your appointment
- 1Could my medicines, my diet or the sample itself explain this?
- 2What does my INR show alongside it?
- 3Should we repeat it before looking further?
Read together with
Doctors rarely read PT alone. These usually sit next to it.
- INRThe clotting time (PT), put on a scale that every lab shares.
- aPTTA clotting time, in seconds, that checks another group of clotting proteins.
- FibrinogenA liver-made protein that forms the mesh of a blood clot.
- PlateletsTiny cell pieces that help the blood clot.
- AlbuminThe main protein in blood, made by the liver.
Quick answers
What is the PT blood test?
PT (Prothrombin time): How many seconds a blood sample takes to form a clot. The lab adds a clotting trigger to the sample and times how long a clot takes to form. This checks clotting proteins made by the liver, several of which need vitamin K to work. The seconds differ from lab to lab more than most tests, so the INR puts them on one shared scale.
What is a normal PT level?
For most adults, PT is typically 11 to 13.5 seconds (varies by lab). Labs differ a little, so the range printed next to your result is the one to go by.
What does a high PT mean?
A PT above the range can mean the blood is clotting a bit more slowly. How far above, the INR, and any blood thinner taken matter more than the seconds alone. Common reasons include taking a blood thinner, especially the kind that blocks vitamin K; a sample tube not filled fully, or a delay before testing; low vitamin K, from a poor diet, some antibiotics or poor absorption; and less often: liver disease, since the liver makes most clotting proteins. A doctor reads it together with your other results and how you feel.
What does a low PT mean?
A PT a little below the range is rarely a concern. It most often reflects the lab's method or how the sample was handled. Common reasons include natural variation between people and between lab methods; how the sample was drawn, stored or handled; and pregnancy, or hormone medicines such as birth control pills.
What can affect my PT result?
An under-filled sample tube or a delay before testing can make the PT read longer than it really is.
What should I ask my doctor about my PT?
Questions worth taking to the appointment: Could my medicines, my diet or the sample itself explain this? What does my INR show alongside it? Should we repeat it before looking further?
What this page can’t do
It reads each number on its own.
Doctors read results together — ALT with AST, ferritin with hemoglobin, TSH with free T4. A pattern says more than any single flag.
It doesn't know you.
Your age, your medicines, how you feel and your last result all change what a number means.
It doesn't remember.
Close this page and your results are gone. That's on purpose: nothing was ever sent to us.
We also make Vita: Health Coach, an app for those parts. It reads your whole report with your medicines and history in mind, answers follow-up questions in plain words, and keeps your reports in one place — for you and for the people you look after.
Vita: Health Coach on the App StoreSources
- MedlinePlus — Prothrombin time (PT)
- MedlinePlus — Prothrombin time test and INR (PT/INR)
- ABIM — Laboratory test reference ranges (January 2026)
Stuck on a word? See the medical words. How we choose our sources. More about Vita Health Coach.