Abstract Number: PB0474
Meeting: ISTH 2021 Congress
Theme: Hemophilia and Rare Bleeding Disorders » Hemophilia - Basic
Background: FVIII inhibitors are immunoglobulins that bind to FVIII molecules reducing the function of the FVIII protein to perform its job, leaving the patient with bleeding episodes. Clinical identification of the presence of FVIII inhibitors has to be confirmed by laboratory testing.
Aims: To assess the large range of results from centres of a UK NEQAS BC FVIII inhibitor exercise by investigating different aspects of the FVIII inhibitor methodology.
Methods: Two lyophilised plasma samples from a donor with haemophilia A, identified as having an inhibitor to FVIII were distributed with different code numbers (S20:04 & S20:05) so that it was not apparent the two samples were identical. Participants were invited to perform a FVIII inhibitor assay using test methods in routine use in their laboratory. Methodology details were requested from centres including;
- Assay used for measurement
- Plasma sample dilutions
- Diluent medium
- FVIII inhibitor methodology
Results: 84 centres returned results of the FVIII inhibitor methodologies used
- Bethesda method (n=25) FVIII inhibitor range = 0.0–7.6Bu/ml
- Nijmegen-Bethesda method (n=24) FVIII inhibitor range= 0.44–4.8 Bu/ml
- Non-classified method (n=35) FVIII inhibitor range = 0.00–4.8Bu/ml
26 different types of dilution combination were used, ranging from single dilution (1in1) to greater than 9 (1in2, 1in 4, 1in8, 1in16, 1in32, 1in64, 1in128 up to 1in2048)
Table 1. FVIII inhibitor results from 82 participants according to what diluent was used.
| Table 1 | ||||
| Type of diluting medium | N | Median FVIII inhibitor (BU/ml) | FVIII inhibitor results (BU/ml) | CV (%) |
| FVIII deficient plasma | 24 | 2.3 | 0.00-4.80 | 200.9 |
| Buffer | 53 | 2.9 | 0.00-7.60 | 195.4 |
| Not stated | 5 | 3.3 | 1.97-4.00 | 196.7 |
Table 1
Figure 1. There was highly significant correlation ( R2=0.72 , p < 1.00) between results obtained on the two samples indicating intra-lab precision and some consistency in how methods were applied locally.
Figure 1
Conclusions: There was considerable variation throughout the FVIII inhibitor assay methods used by participants, with no clear pattern or trend to help explain the wide range of results. The data demonstrate that there is a requirement for appropriate standardisation of the FVIII inhibitor assay to reduce misdiagnosis and potential inappropriate clinical management.
To cite this abstract in AMA style:
Lowe A, Kitchen S, Jennings I, Walker I. Is Standardisation the Key? FVIII Inhibitor Results: A UK National External Quality Assessment Scheme for Blood Coagulation (UK NEQAS BC) Exercise [abstract]. Res Pract Thromb Haemost. 2021; 5 (Suppl 2). https://abstracts.isth.org/abstract/is-standardisation-the-key-fviii-inhibitor-results-a-uk-national-external-quality-assessment-scheme-for-blood-coagulation-uk-neqas-bc-exercise/. Accessed October 1, 2023.« Back to ISTH 2021 Congress
ISTH Congress Abstracts - https://abstracts.isth.org/abstract/is-standardisation-the-key-fviii-inhibitor-results-a-uk-national-external-quality-assessment-scheme-for-blood-coagulation-uk-neqas-bc-exercise/