Factor VIII assay (two-stage chromogenic)

Description: 
Some mutations causing mild haemophilia A can give rise to clinically significant discrepancies between one-stage & two-stage FVIII assays. The two-stage assay involves first generating FXa in a reaction where the patient's FVIII is the rate limiting factor. The second stage involves reacting the FXa generated in the first stage with a chromogenic substrate generating a coloured product, the intensity of which is proportional the the FXa present, which itself is directly proportional to the FVIII actvity.

The chromogenic assay is employed as our routine FVIII activity assay.
Clinical details: 
The complex orchestration of cellular and molecular participants of haemostasis achieves a crucial yet fine balance of procoagulant and anticoagulant mechanisms. Deficiency of a procoagulant integral to the molecular interplay converging on fibrin formation, such as FVIII, reduces ability to form clots and can give rise to a bleeding disorder.
Related condition or disease: 
Haemophilia A, acquired haemophilia
Reference range: 

50 - 150

Units: 
IU/dl
Department: 
Haemostasis and Thrombosis Department
Location: 
St Thomas' Hospital
Sample type and Volume required: 
External requests: Citrated platelet poor plasma
450µL x 1 aliquot
Internal requests: please refer to EPR label

Turnaround time: 
5 - 7 days
Special sample instructions: 

The sample should be analysed or manipulated & stored in the laboratory within 4 hours of venepuncture. Please ensure sample tubes are filled exactly to the fill-line as underfilling creates a dilution error and leads to inaccurate results.

Criteria for acceptance / rejections of sample
Contacts:
Diagnostic Haemostasis and Thrombosis Department
St Thomas': 020 7188 2797; Guy's: 020 7188 7188 ext. 53860
St Thomas' Hospital
North Wing - 4th and 5th Floors
Westminster Bridge Road
London SE1 7EH

Laboratory opening times
24/7

Guy's Hospital
Southwark Wing - 4th Floor
Great Maze Pond
London SE1 9RT

Outside core hours, contact Duty Haemostasis Biomedical Scientist
For clinical advice or interpretation of results, please contact the laboratory in the first instance.
Laboratory: 
Diagnostic Haemostasis and Thrombosis Laboratory at Guy's and St Thomas'

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Last updated: 09/03/2017