Factor Assays: FV111, F1X, FX1, FX11, FV, F11,FV11,FX
Haematology Overview / Directory
Purpose of the test
The body maintains a biological balance between bleeding and clotting. It is able to maintain this balance when the plasma proteins ( blood clotting factors), which are involved, are qualitatively and quantitatively viable.
A shift haemostasis balance may lead to a bleeding diathesis and this shift is usually as result of a reduced amount of a clotting factor.
Intrinsic Pathway factor - use assay based on APTT (VIII, IX, XI and XII).
Extrinsic Pathway and common pathway factors - use assay based on Prothrombin Time (II, V, VII and X)
All coagulation factor bioassays test the ability of dilutions of a standard or test plasma to correct the clotting time of a plasma deficient in the specific factor to be assayed. There is a linear relationship between the clotting time and factor concentration on a log-log plot.
A quantitative assay of an individual clotting factor is required to identify an inherited deficiency and to monitor replacement therapy. Occasionally an assay helps to distinguish acquired defects e.g. DIC, vitamin K deficiency, inhibitors.
Reference Range
Factor II, VII and X
Normal Range 50 - 150 u/dl
Factor V
Normal Range 50 - 150 u/dl.
Factor VIII
Normal Range 50 - 150 u/dl
Factor IX
Normal Range 50 - 150 u/dl
Factor XI
Normal Range 60 - 150 u/dl
Factor XII
Normal Range 40 - 150 u/dl
Infants may have borderline or reduced levels of Vit K dependent factors (II, VII, IX and X).
Sample Requirements
2 Coagulation citrated samples obtained by clean venepuncture.
The sample tube must be correctly filled and there must be no clots, fibrin strands, or haemolysis.
Storage and Transport
The samples must be received in the laboratory within 2 hours of collection.
For Factor VIII assays it is preferable for the sample(s) to be stored on ice immediately after collection and / or brought to the haemostasis section immediately.
Factor VII is sensitive to cold activation. Centrifuge samples at 20°C and keep at room temperature until assay. Snap freeze plasma immediately if stored.
Factor V is very labile. Spin in refrigerated centrifuge and keep in fridge until assay. If not to be assayed within 2 hours separate plasma into plastic tubes and snap
Turnaround Time
The assays are run in regularly batches at least every week.
Results may be available same day by prior arrangement and after discussion with the Haemostasis registrar and the Haemostasis Laboratory on ext 2434
Factors affecting results or interpretation
Clots of any size , haemolysis, underfilling or overfilling will affect result.
Contacts
Haemostasis Laboratory on 020 3299 9000 ext 2434
e-mail: liz.ford@nhs.net
