Prothrombin Time (PT): Measures the time (in seconds) for plasma to clot after adding tissue factor.

International Normalized Ratio (INR): Standardizes PT results across labs, allowing consistent monitoring of anticoagulant therapy.

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).

Analyte: Clotting time (PT) and standardized ratio (INR).

Normal Range:

PT: ~11–15 seconds (varies slightly by lab).

INR: 0.8–1.2 (normal, not on anticoagulants).

Therapeutic INR Range:

2.0–3.0: For most indications (e.g., atrial fibrillation, DVT, PE).

2.5–3.5: For mechanical heart valves.

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

Clinical Use:

Evaluates clotting ability.

Monitors anticoagulant therapy.

Detects bleeding/clotting disorders.