PROTHROMBIN TIME (PT) TEST PROCEDURE

1. Pipette 0.25 ml of the thromboplastin/calcium reagent into a small glass tube. Place in a 37°C water bath for 1–2 minutes.
2. Using a calibrated capillary or delivery pipette, add (0.05 ml) of capillary blood or plasma, mix, and start the stop-watch. Hold the tube in the water bath and tilt the mixture back and forth looking for clot formation. When a clot forms, stop the stop-watch and record the time
3. Convert the clotting time to the INR using the table provided by the manufacturer. Separate INR tables are provided for capillary blood and plasma.

The INR conversion table provided by the manufacturer is specific for The batch of thromboplastin supplied with it.

What is the normal range for Prothrombin time?

11 – 16 seconds

What are Causes of Prolonged PT?

• Treatment with oral anticoagulant drugs (vitamin K antagonists) such as warfarin.
• Liver disease
• DIC
• Haemolytic disease of the newborn
• Rarely a deficiency of factor VII, X, V, or prothrombin.

See also

The principle of prothrombin time test