Can this result diagnose a condition on its own?

No. Laboratory results are interpreted with symptoms, medical history, specimen conditions and related tests.

Which reference range should I use?

Start with the performing laboratory's own reference interval; clinical cutoffs, when relevant, are separate sourced thresholds used for a specific purpose.

When should I discuss the result with a healthcare professional?

Results that are clearly outside range, persistent, symptomatic or unexpected should be reviewed by a healthcare professional.

Information about a laboratory test

Prothrombin Time (PT): What Does This Test Measure?

The Prothrombin Time (PT) test measures how many seconds a blood sample takes to clot, reflecting mainly the extrinsic and common coagulation pathways.

Test summary

Test name: Prothrombin Time (PT)
Abbreviations: PT, Protime
Category: Coagulation
Panel: Coagulation Assessment
Specimen: Citrated plasma
Common units: seconds

What does the test measure?

The Prothrombin Time (PT) test measures how many seconds a blood sample takes to clot, reflecting mainly the extrinsic and common coagulation pathways.

Why is the test ordered?

It may be ordered to investigate abnormal bleeding or clotting, assess coagulation before procedures, or monitor selected anticoagulant therapies.

Information about a low result

A shortened PT is less commonly clinically meaningful and does not diagnose hypercoagulability by itself; specimen, method and related tests matter.

Information about a high result

A prolonged PT means the sample is clotting more slowly and can occur with anticoagulants, liver disease, vitamin K deficiency or coagulation-factor abnormalities.

Reference and clinical context

Start with the performing laboratory's reference interval, unit, specimen type and method. Numeric information on this page is stored as sourced example intervals or clinical thresholds.

Reference range 1

>= 11 – <= 13.5 seconds

Population: Adults not taking anticoagulants
Age range: 18
Specimen: Citrated plasma

Example PT interval without anticoagulation

This is sourced reference/clinical-context information and should not be used alone as a diagnosis or treatment decision. The laboratory report, medication use and clinical context take priority.

Reference ranges may vary by laboratory, method used, age, sex, pregnancy status, and clinical context. The reference range on your own laboratory report takes precedence.

Interpretation notes

PT and INR express related information in different forms, with INR improving standardization across methods. aPTT assesses different coagulation factors and is often interpreted alongside PT.

Related specialties

Hematology
Internal Medicine
Emergency Medicine

Frequently asked questions

More information about this test

Sources

Fibrinogen blood test — U.S. National Library of Medicine (MedlinePlus)
Government medical reference · 2025 · Fibrinogen purpose and example 200–400 mg/dL reference interval · Verified: Aug 12, 2026
D-Dimer Test — U.S. National Library of Medicine (MedlinePlus)
Government medical reference · 2024 · D-dimer use in clot assessment and non-thrombotic causes of elevation including pregnancy · Verified: Aug 12, 2026
Prothrombin Time Test and INR (PT/INR) — U.S. National Library of Medicine (MedlinePlus)
Government medical reference · 2024 · PT/INR purpose, anticoagulation and coagulation interpretation · Verified: Aug 12, 2026
Prothrombin time (PT) — U.S. National Library of Medicine (MedlinePlus)
Government medical encyclopedia · 2025 · Example PT and INR intervals and common warfarin target context · Verified: Aug 12, 2026
Partial Thromboplastin Time (PTT) Test — U.S. National Library of Medicine (MedlinePlus)
Government medical reference · 2026 · aPTT/PTT purpose, prolonged and shortened result context · Verified: Aug 12, 2026