Coagulation factors levels
4.5 mL blood added to 0.5 mL citrate.
Consult pathologist prior to collection.
Clotting assays are based on the ability of test plasma to correct the prolonged clotting time of plasmas with known factor deficiencies.
Activity of test plasma is expressed as % of activity in normal control plasma.
Assays for factors VIII, IX, XI, XII are based on the APTT.
Assays for factors II, V, VII, X are usually based on the PT.
See also Fibrinogen, Factor XIII.
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Typically 50-150% of the activity in pooled normal plasma; alternatively 0.5-1.5 U/mL.
Investigation of patients with a personal and/or family history suggestive of an inherited bleeding disorder.
Factor V deficiency is rare.
Factor VIII and von Willebrand factor assays are required for the diagnosis of von Willebrand disease and haemophilia A and aid in the detection of female carriers of haemophilia A; see von Willebrand disease.
Factor IX assay is required for the diagnosis of haemophilia B (Christmas disease) and aid in detection of female carriers.
Factor XI deficiency is rare and isolated factor VII deficiency very rare.
Factor XII deficiency is not associated with a bleeding tendency.
Other congenital coagulation factor deficiencies are rare, although acquired defects are more common.
Investigation of patients with isolated prolongation of the APTT. This may be seen in the setting of a lupus inhibitor, an acquired factor VIII inhibitor, and congenital deficiencies of factors VIII, IX, XI and XII.
Of these, the lupus inhibitor would be the most common cause.
Detection and quantitation of coagulation factor inhibitors in patients with haemophilia; monitoring coagulation factor replacement therapy.
Coagulation factor assays are only occasionally indicated in the investigation of patients with acquired bleeding disorders, but are required for documentation of acquired inhibitors (usually against factor VIII); see Coagulation factor inhibitors.
Coagulation factor levels are affected by a number of physiological and pathological variables.
Factor VIII (and VWF) levels are increased by oestrogens, eg, during the menstrual cycle, oral contraceptive therapy and pregnancy.
This is particularly important in the diagnosis of mild von Willebrand disease and in the assessment of the female carrier state for haemophilia A.
Bain et al. Dacie and Lewis Practical Haematology. Eleventh edition. 2012.
Knol HM et al. Haemostatic variables during normal menstrual cycle. A systematic review. Thrombosis and Haemostasis 2012; 107: 22-29.