Functional and Immunological Assays of F VIII in 133 Haemophiliacs - Characterization of a Subgroup of Patients with Mild Haemophilia A and Discrepancy in 1- and 2-Stage Assays

Abstract

SummaryA systematic study of the levels of FVIII antigen and activity was done in 133 haemophiliacs. No measurable antigen was demonstrated in the 60 severe haemophiliacs, with the exception of 3 patients with levels ranging between 1.5 and 4.5 U/dl, which corresponded to a dramatic FVIII deficiency. The situation was more complex with the 73 moderate and mild haemophiliacs: 39 of them (53.4%) had a partial, concordant deficiency of both the antigen and the procoagulant activity (1- and 2-stage methods), likely corresponding to a decrease in the synthesis of normal FVIII. The conclusion for the other 34 patients, was a qualitative abnormality of FVIII, the levels of antigen in comparison with the procoagulant activity (1-stage method) appearing to be either very reduced (n = 6) or even nil (n = 8), or on the contrary very much higher (n = 20) or normal. For 11 patients in this last category, we found a clear discrepancy between the procoagulant activity levels obtained with the 2 different techniques, the 1-stage levels being higher than the 2-stage levels. This discrepancy which was stable with restudy on multiple occasions and found in different members of the same families was remedied when vWF was absent in one-stage assay. This suggests that we have identified a variant of haemophilia A with an inherited abnormality of FVIII characterized by an in vitro vWF-dependent expression of procoagulant activity.

A1 Subunit-mediated Regulation of Thrombin-activated Factor VIII A2 Subunit Dissociation

“…These patients originally were identified based on having higher fVIII levels in a one-stage coagulation assay compared with a two-stage coagulation or two-stage chromogenic substrate assay (22,(45)(46)(47)(48). In the one-stage assay, fVIII is activated by thrombin or factor Xa that are formed endogenously during the ϳ45-90 s period between addition of calcium and the formation of the fibrin clot.…”

New developments in laboratory diagnosis and monitoring

“…More than 20% of mild haemophilia A patients are associated with assay discrepancy, where a twofold difference between results obtained with different assay systems is considered as discrepant [1]. In some cases the onestage assay result may be five times higher than the two-stage clotting or chromogenic assay [1].…”

“…Several groups have reported that a subgroup of mild haemophilia A patients have discrepancy between the activity of FVIII as determined using different types of assay [1][2][3]. More than 20% of mild haemophilia A patients are associated with assay discrepancy, where a twofold difference between results obtained with different assay systems is considered as discrepant [1].…”

Personalized Approaches to the Treatment of Hemophilia A and B

“…Currently, discrepancies in factor half-life have been reported between one-stage and two-stage/chromogenic methods in clinical use [50], with the one-stage assay overestimating FVIII levels up to two-to five-fold higher than [51]. In addition, approximately 5-10% of patients with genetically confirmed future science group Review Simhadri, Banerjee, Simon, Kimchi-Sarfaty & Sauna mild HA appear to have normal FVIII activity when assayed with a one-stage method [52].…”