Assay discrepancy in mild haemophilia A

Area of Science:

• Hematology
• Clinical Diagnostics
• Molecular Genetics

Background:

• Factor VIII (FVIII) activity assays are crucial for diagnosing hemophilia A.
• Discrepancies between one-stage and two-stage chromogenic FVIII assays are increasingly recognized in mild hemophilia A.
• These discrepancies, particularly a high one-stage/two-stage ratio, can lead to misdiagnosis.

Purpose of the Study:

• To review assay discrepancy in mild/moderate hemophilia A.
• To estimate the prevalence and impact of diagnostic assay discrepancies.
• To propose recommendations for avoiding misdiagnosis.

Main Methods:

• Review of literature on FVIII assay discrepancies.
• Analysis of mild hemophilia A cases with unique F8 genotypes from Malmö Haemophilia Centre.
• Measurement of FVIII activity using chromogenic and two distinct one-stage assays.

Main Results:

• Significant assay discrepancies observed in approximately one-third of mild hemophilia A patients.
• High one-stage/two-stage FVIII assay ratios are linked to specific FVIII protein structural mutations.
• Inverse discrepancies may correlate with mutations near thrombin cleavage or FIX binding sites.

Conclusions:

• Assay discrepancies pose a risk of misdiagnosing mild hemophilia A.
• Understanding genotype-phenotype correlations is key to interpreting assay results.
• Standardized diagnostic approaches and awareness of potential discrepancies are essential for accurate patient management.