Coagulation factors

Last updated: Thursday, 06, April, 2006

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Item Process
Specimen

4.5 mL blood added to 0.5 mL citrate.

Consult pathologist prior to collection.

Method

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 - plasmaFactor XIII.

Reference Interval

Typically 50-150% of the activity in pooled normal plasma; alternatively 0.5-1.5 U/mL.

Application
  1. Investigation of patients with a personal and/or family history suggestive of an inherited bleeding disorder.
    Factor VIII and von Willebrand factor assays are required for the diagnosis of von Willebrand’s disease and haemophilia A and aid in the detection of female carriers of haemophilia A; see von Willebrand factor antigen (VWF:Ag).
    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.
  2. 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.
  3. 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.
Interpretation

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 or pregnancy.
Baseline levels can only be assessed if specimens are collected during menstruation.
This is particularly important in the diagnosis of mild von Willebrand’s disease and in the assessment of the female carrier state for Haemophilia A.

Consult pathologist.

Reference

Dacie JV and Lewis SM. Practical Haematology. 8th ed. Churchill Livingstone 1995.