РусскийEnglishEspañol — próximamenteFrançais — bientôtDeutsch — in VorbereitungItaliano — in arrivoAll languages
Prothrombin time
Core test of the extrinsic clotting pathway and the basis for the INR — the standard monitor of warfarin therapy.
Other names: PT, pro timeSection: Blood clotting
Updated: August 31, 2026·MedProtect editorial team Reference information — not a diagnosis or a prescription
In shortProthrombin time measures how long blood takes to clot via the extrinsic pathway. A typical reference is 11–13.5 seconds. Prolongation suggests factor deficiency, liver disease, vitamin K deficiency, or warfarin effect. The PT is converted to the INR for standardized monitoring.
Reference ranges
Group
Reference range
Typical reference — typical range (international reference, not a national standard)
11–13.5 seconds
Range from the MedlinePlus Medical Encyclopedia (international reference, not a national standard). The report's own interval applies; for warfarin monitoring the INR matters more than seconds. Reference ranges vary between laboratories and assays — use the range printed on your own lab report.
Check your value
Enter the number from your lab report — see how it compares with the typical range. Mind the units shown in the chosen row.
A rough comparison with a typical range, not a diagnosis. Reference ranges vary between laboratories — check the range on your own report and let a clinician interpret the result.
What this marker is
The test adds tissue factor to a blood sample and times clot formation. It depends on factors II, V, VII, X and fibrinogen — the factors most sensitive to warfarin and to liver synthetic function.
Because reagents differ between laboratories, results are standardized as the INR (international normalized ratio). People on warfarin are managed by INR targets rather than raw seconds.
When it is high
Warfarin effectThe intended action of the drug; the dose is adjusted to keep the INR in the target range.
Liver diseaseThe liver makes most clotting factors, so reduced synthesis prolongs the PT.
Vitamin K deficiencyVitamin K is needed to activate several factors; deficiency prolongs the PT.
When it is low
Short PTUsually not clinically meaningful; rarely seen with high factor levels or sample issues.
What can skew the result
These factors can shift the value without any disease — worth considering before a retest:
Warfarin and other anticoagulantsVitamin K intake in food and supplementsLiver diseaseAntibiotic courses
How to prepare
Blood from a vein into a citrate tube; a full, correctly mixed tube matters. People on warfarin test on a regular schedule set by the provider.
When a retest makes sense
On warfarin — on the provider's schedule. An isolated unexpected prolongation is usually repeated within 1–2 weeks with liver tests.
Who usually reviews this result
A result outside the reference range is usually reviewed by: your GP or primary care doctor; a hematologist for clotting disorders. Bring your lab report and any previous results to the appointment.
Names used on lab reports
Your report may use any of these names: Prothrombin timePTPro timeINR (derived)
Units
Measured in: seconds
Several markers on your report?
See how MedProtect explains results in the app: the whole report, a check of the recognized values, and a clear breakdown.
We use cookies and Yandex.Metrika for visit statistics — no advertising tracking and no session recording. The counter loads only after your consent. Privacy policy.