Factor X Activity
Stuart Prower Factor
Evaluate an isolated, prolonged PT, evaluate prolongation of both the aPTT and PT, and to document factor X deficiency
To evaluate an isolated prolonged PT or to evaluate prolongation of both the APTT and PT and to document factor X deficiency. Factor X is a 54.8 kilodalton vitamin K-dependent glycoprotein coagulation factor that is produced by the liver. Normal factor X’s plasma concentration is approximately 10 mg/mL and half-life is about 40 hours. Factor X activation occurs by both the extrinsic and intrinsic pathways. Factor X deficiency should be considered when a patient with bleeding history has both extended protime (PT) and activated partial thromboplastin time (aPTT). The dilute Russell viper venom (dRVVT) measures the activation of factor X and will be prolonged in patients with deficiency. Congenital factor X deficiency is rare and is inherited as an autosomal recessive trait. This condition affects both males and females. A few cases of combined congenital factor II, VII, IX, and X factor deficiencies have been reported.
Acquired deficiencies occur with significant hepatic dysfunction, with vitamin K antagonist (warfarin) therapy, and in individuals with vitamin K deficiency. Factor X deficiency may be associated with primary systemic amyloidosis. Isolated factor X deficiency may also occur in patients with respiratory infections, acute myeloid leukemia, amyloidosis, and with other malignancies. Acquired specific factor X inhibitors are rare in patients without congenital deficiency. Symptoms (homozygotes) include hematoma formation, postsurgical hemorrhage, menorrhagia, hematuria, and umbilical cord hemorrhage. Factor X plasma activity <30% may result in excessive bleeding following a traumatic event. Spontaneous bleeding similar to that observed in severe hemophilia may occur when the activity is <1%.
Blue-top (sodium citrate) tube
Ideally, the patient should not be on anticoagulant therapy. Avoid warfarin (Coumadin®) therapy for two weeks prior to the test and heparin, direct Xa, and thrombin inhibitor therapies for about three days prior to testing.
Blood should be collected in a blue-top tube containing 3.2% buffered sodium citrate. Evacuated collection tubes must be filled to completion to ensure a proper blood-to-anticoagulant ratio. The sample should be mixed immediately by gentle inversion at least six times to ensure adequate mixing of the anticoagulant with the blood. A discard tube is not required prior to collection of coagulation samples unless the sample is collected using a winged (butterfly) collection system. 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. When noncitrate tubes are collected for other tests, collect sterile and nonadditive (red-top) tubes prior to citrate (blue-top) tubes. Any tube containing an alternative anticoagulant should be collected after the blue-top tube. Gel-barrier tubes and serum tubes with clot initiators should also be collected after the citrate tubes.
Severe hemolysis; improper labeling; clotted specimen; specimen diluted with IV fluids; samples thawed in transit; improper sample type; sample out of stability
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