The presence of a factor deficiency in the extrinsic and/or common pathway can be detected by performing a Prothrombin Time (PT) on a mixture of patient plasma and normal pool without incubation. A factor deficiency is indicated if the normal plasma corrects the elevated PT of the patient sample.
The 9:1 blood/citrate ratio must be kept constant. Adjustments for the amount of anticoagulant should be made when the hematocrit is abnormal (above 55%). Mix immediately to prevent clotting.
Collection Instructions
Send whole blood sample(s) at room temperature as soon as possible.
If specimens cannot be shipped immediately, centrifuge and separate plasma within 1 hour of collection, send frozen plasma on dry ice
PT mixing studies are not performed:
- if the PT falls within the normal PT Reference Interval. See Reporting.
- if the patient is on heparin or oral anticoagulant therapy. See Reporting.