Comprehensive comparison of global coagulation assays to differentiate lupus anticoagulant from acquired hemophilia A in patients with prolonged APTT.

There is no established method for differentiating acquired hemophilia A (AHA) from lupus anticoagulant (LA) positivity because both present with prolonged activated partial thromboplastin time. We compared various parameters of rotational thromboelastometry (ROTEM), thrombin generation assay (TGA), and clot waveform analysis (CWA) in patients with AHA (n = 10) and LA (n = 44). Compared with AHA, possible (n = 12) and definite (n = 32) LA showed significantly shorter clotting time (CT) in NATEM mode of ROTEM (> 3600 vs. 501/533). In TGA, peak height was significantly lower in AHA (16 vs. 242/174 nM). In CWA, CT was significantly longer (81 vs. 36/41 s) and Ad|min1| was lower (2.1 vs. 8.7/6.7) in AHA. Notably, CT by NATEM and peak height in TGA completely discriminated between AHA and LA, whereas Ad|min1| did not discriminate between them in 4 cases of AHA and 1 of LA. Comparison of 3 patients with both AHA and LA against a patient with only LA and markedly low FVIII activity (3.5%) showed that both CT by NATEM and peak height of TGA precisely classified the former 3 cases as AHA and the latter 1 case as LA, whereas Ad|min1| classified all 4 cases as AHA. ROTEM and TGA can comparably distinguish between AHA and LA.

In vitro validation of chromogenic substrate assay for evaluation of surrogate FVIII-activity of emicizumab.

[Introduction] Emicizumab, a bispecific antibody mimicking activated factor VIII (FVIII), is increasingly used in prophylaxis against bleeding in hemophilia A. Human factor-based chromogenic substrate assay (hCSA) shows concentration-dependency between emicizumab and reported FVIII activity. However, the assay measurement settings have not been optimized for emicizumab, and the reported FVIII activity cannot be directly referred as surrogate FVIII activity. [Materials and Methods] For in vitro validation of hCSA-reported surrogate FVIII activity, we compared the equation curves for emicizumab concentration with surrogate FVIII activity using spiked plasma in the thrombin generation assay (TGA), hCSA, and clot waveform analysis (CWA). Then, we generated conversion equations for hCSA-reported surrogate FVIII value to that of TGA. We also assessed the additive effect of rFVIII onto 340 nM (i.e., 50 µg/mL) emicizumab using the same assays. [Results] With 1:20 diluted plasma, halving hCSA-reported surrogate FVIII activity can be approximated to that in TGA triggered by the extrinsic pathway reagent (27.3 IU/dL vs. 13.9 IU/dL) under therapeutic emicizumab concentration. Both in TGA and hCSA, the additive effect of added FVIII on therapeutic emicizumab concentration (340 nM) was maintained at low levels of FVIII but gradually decreased at higher levels. [Conclusions] Surrogate FVIII activity can be estimated simply by halving hCSA-reported FVIII value, and the additive effect of FVIII on emicizumab diminishes at high concentrations. Based on our in vitro study, a clinical study is currently being conducted to compare individual variation of surrogate FVIII activity in hCSA and TGA.

Combination therapy with von Willebrand factor concentrate plus recombinant factor VIII during cesarean section in a patient with type 3 von Willebrand disease and a low inhibitor titer: a case report.

Type 3 von Willebrand disease (VWD), a rare and severe subtype, can produce inhibitors in roughly 5% to 10% of cases. We present a case of type 3 VWD with inhibitors in late pregnancy, which was successfully managed with a combination of neutralization and factor (F)VIII replacement during cesarean delivery. The patient, a 30-year-old woman, had no history of inhibitors despite over 100 exposures to VWF/FVIII. She developed inhibitors after 28 weeks of weekly pd VWF/FVIII prophylaxis for recurrent urolithiasis-associated hematuria during pregnancy. Genetic analysis detected two novel frameshift mutations: VWF Exon7 c.777_784dup and Exon14 c.1625_1646del. Titers of inhibitors to factors VIII and VWF using the Bethesda assay were 1.2 and 1.1 BU/mL, respectively. Pharmacokinetics revealed significantly low in vivo recovery of FVIII:C and VWF:Rcof and shortened half-life. During cesarean delivery, a combination of bolus pd VWF/FVIII once daily for neutralizing inhibitors plus continuous infusion of recombinant FVIII Fc fusion protein resulted in minimal bleeding without allergic reactions. Both VWF:Rcof and FVIII:C levels increased transiently during the 7-h of combination therapy without thrombotic events. In conclusion, combination therapy with neutralization and continuous FVIII replacement was effective for hemostasis with a low VWD inhibitor titer, though further optimization is required.