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A Case of Discrepant One-stage and Chromogenic Factor VIII Activity Assay in a Patient with a Hemizygous Arg550His Mutation in the F8 Gene

J. Hancock1, E. Li2, J. Larson1, N. Montanez2, M. Escobar3

1The University of Texas Health Science Center at Houston, Houston, Texas, United States, 2The University of Texas Health Science Center at Houston, McGovern Medical School, Gulf States Hemophilia and Thrombophilia Center, Houston, Texas, United States, 3University of Texas Health Science Center, Houston, Texas, United States

Abstract Number: PB0665

Meeting: ISTH 2022 Congress

Theme: Hemophilia and Rare Bleeding Disorders » Hemophilia - Clinical

Background: Missense mutations in the F8 gene are known to cause discrepant one-stage and chromogenic assays of Factor VIII (FVIII) activity. Lower FVIII activity (>2-fold difference) when measured with the chromogenic substrate assay compared to the one-stage assay has been described with mutations in the A1-A2-A3 domains of F8. These mutations are thought to disrupt FVIII heterodimer stability and FVIIIa heterotrimer stability.

Aims: We describe a clinical case of discrepant one-stage and chromogenic substrate assay for factor VIII activity in a patient with mild Hemophilia A with a c.1649G>A(p.Arg550His) mutation in the F8 gene.

Methods: The electronic medical record was retrospectively reviewed.

Results: A 50-year-old man with prior history of hemarthrosis, recurrent epistaxis, prolonged bleeding with skin lacerations and prolonged bleeding after tooth extraction presented to our center for evaluation. He had a normal INR of 1.16 and mild prolongation in PTT of 43.8 that fully corrected on mixing study. He had a normal Thrombin Time. He had multiple prior one-stage assays of FVIII activities that ranged from 57-71%. At the time of evaluation, his one-stage FVIII assay was 57%. A chromogenic FVIII activity was checked and found to be 27%. The patient was given a diagnosis of mild Hemophilia A and genetic testing was ordered. He was found to have a hemizygous missense mutation for a c.1649G>A (p.Arg550His) in exon 11 of the F8 gene, consistent with mild Hemophilia A.

Conclusion(s): The c.1649G>A (p.Arg550His) mutation in F8 has been described to cause discrepant results between one-stage and chromogenic substrate assays along with other missense mutations in the A1-A2-A3 domain interfaces, and chromogenic assays should be considered in patients with high clinical suspicion for Hemophilia A even with a normal one-stage FVIII activity assay.

To cite this abstract in AMA style:

Hancock J, Li E, Larson J, Montanez N, Escobar M. A Case of Discrepant One-stage and Chromogenic Factor VIII Activity Assay in a Patient with a Hemizygous Arg550His Mutation in the F8 Gene [abstract]. https://abstracts.isth.org/abstract/a-case-of-discrepant-one-stage-and-chromogenic-factor-viii-activity-assay-in-a-patient-with-a-hemizygous-arg550his-mutation-in-the-f8-gene/. Accessed December 6, 2023.

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