Abstract
In recent years, there has been greater awareness among hemostasis scientists and
clinicians that factor VIII coagulant activity (FVIII:C) measured in certain patients
with mild hemophilia A can show different results depending on the assay system. A
subgroup of mild hemophilia families have a method-related discrepancy in FVIII:C
results, whereby the one-stage clotting assay (FVIII:C-1) is significantly higher
than the two-stage clotting assay (FVIII:C-2) or the chromogenic assay (FVIII:C-chr).
To identify such patients, the routine laboratory can use automated procedures for
the FVIII:C-chr to replace the complex, manual FVIII:C-2 method. Laboratories must
employ appropriate quality management to ensure accurate and precise results, especially
in the abnormal range. This discrepant phenotype of hemophilia A is seen in up to
40% of mild hemophilia A cases and represents a clinically significant bleeding disorder.
A small proportion of these cases have FVIII:C-1 within the normal range and risk
a missed diagnosis if the FVIII:C-chr is unavailable. Other patients may be mismanaged
if FVIII:C-1 gives an overestimate of FVIII:C and their bleeding risk is consequently
underestimated. Affected family members in the discrepant group of patients have a
limited range of FVIII (F8) gene missense mutations, causing alterations of the structure of the A1, A2, or
A3 domains of FVIII. Therefore, both FVIII:C-chr and F8 gene mutation analysis are recommended to confirm the diagnosis of mild hemophilia
A and assist with decisions about the patient's phenotype.
Keywords
factor VIII - hemophilia A - discrepant - assay methods
