Factor X Activity

Plasma, frozen

1 mL

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.

This test is used to evaluate an isolated, prolonged PT, evaluate prolongation of both the aPTT and PT, and to document factor X deficiency.^6-8

Direct Xa or thrombin inhibitor therapy may cause factitiously low results.

Factor X activity is determined using an aPTT-based one-stage clotting time assay. Factor X-depleted plasma is used as the substrate, and the clotting time with the patient plasma is compared to the clotting time of normal pooled plasma.

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