Overview:

• Measures how long it takes blood to clot.

• Evaluates the extrinsic and common coagulation pathways.

• INR (International Normalized Ratio) standardizes PT results across labs.

• Commonly used to monitor patients on anticoagulant therapy (e.g., warfarin).

Risk Assessment / Clinical Use:

• Detects bleeding/clotting disorders.

• Monitors warfarin therapy.

• Assesses liver function (since clotting factors are produced in the liver).

• Helps in pre-surgical screening for bleeding risk.

Normal Range:

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

• INR: 0.8 – 1.2 (therapeutic range for patients on warfarin is usually 2.0 – 3.0, and 2.5 – 3.5 for mechanical heart valves).

Interpretation:

• Prolonged PT/High INR: Liver disease, vitamin K deficiency, warfarin therapy, DIC, coagulation factor deficiency.

• Shortened PT/Low INR: Rare, may suggest high clotting tendency.

Sample Type:

• Venous blood (collected in a citrate anticoagulant tube).