The Basics of Prothrombin Time

Prothrombin time was described by Quick in 1935. It is the time taken by re-calcified plasma to clot in the presence of tissue procoagulant extract known as thromboplastin. It asses the efficiency of the extrinsic coagulation system. The test depends on activation of factor X by factor VII by tissue factor.

The details of the method are beyond the scope of this text. The outline is as follows. Thromboplastin is added to plasma that has been separated from blood collected in sodium citrate and allowed time to mix. To this mixture calcium chloride is added. The time taken for the plasma to clot is the prothrombin time. The end point (clotting) may be determined manually or using automated (optical or magnetic) methods.

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Prothrombin Time 

Source: All about blood
Image credits: All about blood

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