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Test ID: BIA Anti-Factor FVIII
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Bethesda Inhibitor Assay Anti-Factor FVIII
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Useful For
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To detect and determine the presence and titer of a specific factor inhibitor directed against coagulation factor VIII.
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Method name and description
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Turbidimetric
Test is performed using Sysmex CS5100.The Bethesda assay is based on the ability of the patient’s plasma containing factor VIII inhibitor to inactivate factor VIII present in normal pooled plasma (NPP). Dilutions of the patient’s plasma are incubated with NPP for 2 hours at 37 ºC, and then the residual factor VIII is measured. Although the Bethesda assay is commonly performed for detection of an inhibitor to factor VIII, it can also be used to quantify inhibitors to factor V and factors IX, X, XI and XII
Inhibitors are measured in Bethesda Units (BU). One BU is defined as the quantity of inhibitor that neutralizes 50% of the factor VIII in normal plasma in 2 hours at 37ºC.
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Reporting name
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BIA inhibitors Anti- FVIII
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Clinical information
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Significant bleeding can result from the presence of a coagulation factor inhibitor and could be life-threatening. Whether the inhibitor is present due to hemophilia or of an acquired nature, it greatly complicates the treatment process of a decreased factor level. The titer of the inhibitor may determine the mode of treatment. Bethesda units are a standardization to give a uniform definition of an inhibitor.
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Specimen type / Specimen volume / Specimen container
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Plasma Na Cit. Platelet-poor plasma.
Specimen Volume:2.7 ml.
Container/Tube: Light-blue top (citrate)
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Collection instructions / Special Precautions / Timing of collection
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Sample collected in HMC facilities/others and transported to the lab within 1hour :
• Collect sample into light blue-top (sodium citrate).
• Tubes must be filled to within +/- 10% of their proper volume, to provide a 9:1 ratio of blood to citrate.
2- Samples collected in HMC facilities / others and which are expected not to reach the lab within 1hour:
• Centrifuge the whole blood and carefully remove the plasma by pipette not by decanting and send the plasma in a temperature-controlled environment (18-25ºC ) within one hour of centrifugation.
• If the transportation of the plasma can’t be within a maximum of 2hour , prepare platelet-poor plasma as follow:
A: Re-centrifuge plasma again.
B: Remove the top portion of plasma leaving approximately 250 mcL in the bottom to discard.
C: The double-centrifuged plasma should be aliquoted (0.5 to 1 mL per aliquot) into labeled plastic tubes. The number of tests ordered will determine the aliquots needed.
D: Freeze immediately at -20 ºC or below .
E: Specimens must arrive frozen.
3- Sample for Platelets function studies (Platelets function assay) , Citrated whole blood should reach HMC within a maximum of 1-2 hours of collection.
4- For heparin monitoring, follow the above mentioned steps.
5- Consider patient HCT %. , if HCT is >55%, the volume of anticoagulant in the tube must be adjusted by the referring lab, as per the below table shows the volume of citrate (µL) to be removed from common sizes of coagulation specimen tubes prior to specimen collection. After removal of the specified volume of citrate, enough blood is added to fill the tube to the ideal volume.
| Hematocrit % |
Volume to be removed, µL |
| 2.7 ml Tube |
1.0 ml Tube |
| 56 |
50 |
20 |
| 57 |
50 |
20 |
| 58 |
60 |
20 |
| 59 |
60 |
20 |
| 60 |
70 |
30 |
| 61 |
70 |
30 |
| 62 |
80 |
30 |
| 63 |
80 |
30 |
| 64 |
90 |
30 |
| 65 |
90 |
30 |
| 66 |
100 |
40 |
| 67 |
100 |
40 |
| 68 |
110 |
40 |
| 69 |
110 |
40 |
| 70 |
120 |
40 |
| 71 |
120 |
40 |
| 72 |
130 |
50 |
| 73 |
130 |
50 |
| 74 |
140 |
50 |
| 75 |
140 |
50 |
| 76 |
150 |
50 |
| 77 |
150 |
60 |
| 78 |
160 |
60 |
| 79 |
160 |
60 |
| 80 |
170 |
60 |
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Relevant clinical information to be provided
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Patient/family history of bleeding disorder. History of anticoagulant therapy. History of chronic diseases
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Storage and transport instructions
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Specimen Rejection Criteria
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Specimens with no label or missing required identification
Broken, leaking or contaminated specimen
Clotted samples
Under-filled or overfilled sample tubes.
Wrong sample container sample received
Improper specimen transport temperature (e.g. like specimens which are needed to be sent on ice)
Old specimen (test-dependent)
Grossly Hemolyzed sample (test-dependent)
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Biological reference intervals and clinical decision values
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Factors affecting test performance and result interpretation
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No interference up to:
Triglycerides 3028 mg/dL.
Hemoglobin 200 mg/dL.
Bilirubin 48 mg/dL.
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Turnaround time / Days and times test performed / Specimen retention time
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For routine ordered test : 3 working days
For stat ordered test :
- During the Laboratory working hours from 0700 hours to 1500 hours (Sunday to Thursday): TAT is Within 8hrs.
- After duty hours, weekends and on holidays: TAT is within 12 hrs. with the following requirements:
- Laboratory should be notified by telephone about the sending of a STAT sample.
- The sample should be hand-delivered to the central processing area and requesting them to deliver it immediately to the hematology coagulation lab.
Test is done : Daily.
Specimen retention time: NA
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