Factor IX inhibitor (Bethesda)

Dilutions of test plasma (i.e. reducing concentrations of inhibitor) are incubated for a short period (30 minutes) at 37oC in the presence of a fixed amount of exogenous FIX in the Bethesda assay. One unit of inhibitor is defined as the amount of inhibitor that will neutralise 50% of a normal plasma containing 100% FIX. The amount of residual FIX in each tube is used to calculate the inhibitor level.
Clinical details: 
Acquired inhibitors to FIX are antibodies that arise in 1.5 - 3% of patients with hereditary haemophilia B as a result of recognising therapeutic FIX products as 'foreign' protein, or very rarely, in patients with previously normal haemostasis as part of an autoimmune process. Inhibitors in congenital haemophiliacs complicate treatment as the infused FIX has a shorter survival time, and patients with acquired haemophilia can present with severe bleeding.
Reference range: 

Not detected

Sample type and Volume required: 
External requests: Citrated platelet poor plasma
1mL x 1 aliquot
Internal requests: please refer to EPR label

Turnaround time: 
7 - 10 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.

Diagnostic Haemostasis and Thrombosis Department
020 7188 2797
St Thomas' Hospital
North Wing - 4th and 5th Floors
Westminster Bridge Road
London SE1 7EH

Laboratory opening times
For clinical advice or interpretation of results, please contact the laboratory in the first instance.

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Last updated: 09/03/2017