Prothrombin is a clotting factor produced by the liver and dependent on vitamin K.

The PT test measures the time taken for plasma to clot after adding tissue factor.

Clinical uses include:

Monitoring patients on warfarin therapy.

Detecting bleeding disorders due to clotting factor deficiencies.

Assessing liver disease and vitamin K deficiency.

Supporting diagnosis of disseminated intravascular coagulation (DIC).

PT is often reported with INR (International Normalized Ratio) for standardized comparison across labs.

Analyte: Time (in seconds) for blood plasma to clot.

Normal Range: Approximately 11–15 seconds (varies by lab).

INR Range:

Normal: 0.8–1.2

Therapeutic (on warfarin): 2.0–3.0 (higher for mechanical heart valves).

Prolonged PT: May indicate liver disease, vitamin K deficiency, clotting factor deficiency, or anticoagulant therapy.

Shortened PT: Rare, may suggest increased clotting tendency.

Clinical Use:

Evaluates clotting ability.

Monitors anticoagulant therapy.

Detects bleeding/clotting disorders.