Laboratory testing in hemophilia: Impact of factor and non‐factor replacement therapy on coagulation assays

Abstract

The advent of extended half‐life (EHL) recombinant clotting factors and innovative non‐factor replacement therapeutics, such as emicizumab, offers several advantages over existing products for the prophylactic treatment of people living with hemophilia (PwH). These include low annual bleeding rates with less frequent dosing, higher trough plasma concentrations, and a more convenient route of administration. However, increasing use of these therapies poses challenges to clinicians and coagulation laboratories due to the lack of standardized assays for monitoring of hemostatic parameters, and the potential for misinterpretation of test results, which may jeopardize patient safety. Definitive diagnosis of hemophilia and treatment monitoring is reliant on demonstrating factor VIII (FVIII; hemophilia A) or factor IX (FIX; hemophilia B) deficiency using a functional coagulation assay. The most frequently used assays are based on activated partial thromboplastin time, using a one‐stage or two‐stage process. While one‐stage and chromogenic assays have performed well with human‐derived FVIII and FIX and full‐length recombinant products, EHL recombinant factors are heterogeneous in structure and mode of action and therefore show wide variation in activity levels between different one‐stage assays, and between one‐stage and chromogenic assays. In the context of the recommended stepwise approach for laboratory diagnosis of hemophilia, we examine the diagnostic challenges associated with the use of EHL factors and novel non‐factor therapeutics and consider the optimal diagnostic approach in PwH who are receiving these treatments. Ultimately, accurate diagnostic solutions are a prerequisite for personalized therapy to minimize treatment burden and improve quality of life in PwH.

Should emicizumab be used in patients with acquired hemophilia A?

“…Effects on standard laboratory tests also need to be considered in this scenario. In the presence of emicizumab, the APTT is artificially shortened and APTT‐based clotting factor assays and inhibitor tests cannot be used 22,23 . This is important during follow‐up to detect remission and potential recurrence of AHA.…”

Extended Half-Life Factor VIII/Factor IX Products: Assay Discrepancies and Implications for Hemophilia Management

“…This awareness is proven by the quantity of conducted field and also by smaller, local studies and the continuously growing number of corresponding original articles, reviews, and guidelines. 11,12,18,[22][23][24][25] The potential applicability of available OSC (aPTT reagents) or CS assays for the accurate determination of particular EHL factor activity may be assessed by studying corresponding publications. In fact, the impact of several EHL products, especially on particular OSC assays, is to such an extent that resulting mismeasurements occur independent of the applied assay platform.…”

“…[8][9][10] This situation has been further complicated by the introduction of modified recombinant factor concentrates with extended half-life (EHL; typically $ 1.5-fold for FVIII and $ 5-fold for FIX) that additionally cause aPTT reagent-dependent assay discrepancies. 11,12 In the present in vitro study, we assessed the accuracy of different OSC and CS assays with respect to the analysis of available EHL-FVIII and EHL-FIX concentrates on the Siemens Atellica COAG 360 analyzer. 13 The results are discussed in light of the recent literature and illustrate the need for EHL-FVIII-/FIX productspecific laboratory requests to adequately address observed assay discrepancies.…”

Emicizumab (Hemlibra®) in hemophilia A patients with inhibitors against factor VIII — guidelines of the Group for Haemostasis of the Polish Society of Haematology and Transfusion Medicine

“…It was therefore necessary to go back to BPAs [10]. Table 2 presents the effect of emicizumab on the parameters of selected laboratory coagulation tests [29][30][31]. Emicizumab reduces the activated partial thromboplastin time (APTT) and may therefore be responsible for false APTT-dependent coagulation assay results, factor VIII activity included.…”

“…There may also appear problems with interpretation of coagulation test results for such patients because emicizumab effects the APTT measurement. Selection of appropriate laboratory assay for monitoring haemostatic parameters may also be a challenge in everyday clinical practice [29][30][31].…”