Factor X Activity

This test is used to evaluate an isolated prolonged PT or to evaluate prolongation of both the APTT and PT and to document factor X deficiency.^6-8 Factor X is a 54.8 kilodalton vitamin K-dependent glycoprotein coagulation factor that is produced by the liver.⁶ Normal factor X's plasma concentration is approximately 10 mg/mL and half-life is about 40 hours.⁶ 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.^7,8 Congenital factor X deficiency is rare and is inherited as an autosomal recessive trait.⁶ This condition affects both males and females.⁶ A few cases of combined congenital factor II, VII, IX and X factor deficiencies have been reported.⁶

Acquired deficiencies occur with significant hepatic dysfunction, with vitamin K antagonist (warfarin) therapy and in individuals with vitamin K deficiency.^6,7 Factor X deficiency may be associated with primary systemic amyloidosis.^6,8 Isolated factor X deficiency may also occur in patients with respiratory infections, acute myeloid leukemia, amyloidosis and with other malignancies.⁷ Acquired specific factor X inhibitors are rare in patients without congenital deficiency.^6,7 Symptoms (homozygotes) include hematoma formation, postsurgical hemorrhage, menorrhagia, hematuria and umbilical cord hemorrhage.^6,7 Factor X plasma activity <30% may result in excessive bleeding following a traumatic event.⁶ Spontaneous bleeding similar to that observed in severe hemophilia may occur when the activity is <1%.^6,7