Specific inhibitors of extrinsic pathway factors are extremely rare, but may produce a prolonged PT. Diminished levels of all the factors of the extrinsic pathway can also occur in consumptive coagulopathies, such as disseminated intravascular coagulation (DIC), and as the result of decreased factor production as can be seen with severe liver disease or malnutrition. Acquired deficiencies of the vitamin K-dependent factors II and VII may occur during warfarin therapy and in patients with vitamin K deficiency. Refer to individual test descriptions for more information. Congenital deficiencies of these factors are relatively rare and cause bleeding disorders of varying severity. 6-8 The PT is more responsive to deficiencies of factors X and V than is the aPTT. The PT is sensitive to deficiencies of extrinsic and common pathway factors X, VII, V, II, and fibrinogen. The use of low ISI thromboplastin serves to improve the precision of therapeutic monitoring by enhancing sensitivity of the prothrombin assay. The ISI of the thromboplastin used in the LabCorp assay is near 1.0. Each thromboplastin is assigned an activity Index (ISI) based on comparison to an international reference thromboplastin from the World Health Organization. The INR serves to normalize results obtained from different laboratories for the variable responsiveness of different thromboplastin reagents. Prothrombin time results are reported in seconds and are also converted to international normalized ratio (INR) values. This serves to increase the PT assay's sensitivity for factor efficiencies.
Toem testing free#
Recombinant tissue factor is free from contamination with coagulation factors that can be found in tissue factor extracted from other sources. The thromboplastin reagent used by LabCorp consists of recombinant tissue factor mixed with synthetic phospholipid. Please print and use the Volume Guide for Coagulation Testing to ensure proper draw volume. Gel-barrier tubes and serum tubes with clot initiators should also be collected after the citrate tubes. Any tube containing an alternative anticoagulant should be collected after the blue-top tube.
4,5 When noncitrate tubes are collected for other tests, collect sterile and nonadditive (red-top) tubes prior to citrate (blue-top) tubes. With a winged blood collection set a discard tube should be drawn first to account for the dead space of the tubing and prevent under-filling of the evacuated tube. A discard tube is not required prior to collection of coagulation samples unless the sample is collected using a winged (butterfly) collection system. 2,3 The sample should be mixed immediately by gentle inversion at least six times to ensure adequate mixing of the anticoagulant with the blood. 1 Evacuated collection tubes must be filled to completion to ensure a proper blood-to-anticoagulant ratio. Blood should be collected in a blue-top tube containing 3.2% buffered sodium citrate.
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