Thrombin Generation Assay and by-Passing Therapies in Patients with Inhibitors,
Authors: Kavakli Kaan , Ay Yilmaz , Karapinar Deniz Yilmaz , Balkan Can 
Published: October 2019

Abstract
Abstract 3322
No routine test is available for monitoring bypassing agent therapy in patients with inhibitors. General clotting tests such as PT, aPTT and factor activities do not reflect overall thrombin generation and are insensitive to hypercoagulation and hypocoagulation.
In this study, we aimed to investigate the importance of thrombin generation assay (TGA) in monitoring hemostasis during factor supplementation in hemophilia patients with and without inhibitor. Study group consisted of 39 patients (27 hemophilia A, 8 hemophilia B, one vWD-3, two FVII def. and one FX def.). All patients were male. Seven out of 27 hemophilia A patients had an inhibitor. The mean age was 17±9.7 years (range: 3–55). A total of 59 (inhibitor positive=19) bleeding episodes and/or surgical interventions were evaluated. Acute bleeding episodes were classified as acute hemarthrosis (n=21), soft tissue hemorrhages (n=6), oral /nasal hemorrhages (n=7), hematuria (n=2) or GIT hemorrhages (n=3). Twenty major or minor surgical interventions were classified as radioisotope synovectomy (n=11), teeth extractions (n=2), circumcision (n=1), port-a-cath removal (n=1); hemorrhoid operation (n=1) or open synovectomy and arthroplasty n=4). rFVIIa and aPCC therapies were administered to inhibitor-positive patients. PPP was always prepared within 30 min of venipuncture. PT, aPTT and FVIII activities were measured in plasma from citrated blood samples taken before treatment of patients for bleeding or for surgery preparation. Before TGA test, aliquoted PPP was stored for 3 months at −80°C, and all samples were assessed together. Lab parameters were evaluated at basal levels and after 1 hour of factor therapy. These tests were repeated when clinical hemostasis was obtained within 24 hours of the post-op period. PT, aPTT, FVIII activities were assessed by Siemens kits with CA-1500 (Sysmex–Siemens). The Calibrated Automated Thrombogram (CAT; Thrombinoscope BV, Maastricht, The Netherlands) method was used for the TGA.
No difference was found between 1th and 24th hour clinical responses after rFVIIa and aPCC treatment (P= 0.96) in hemophilic patients with inhibitor. Basal, first hour and 24th hour TGA lag time values were significantly shorter in hemophilic patients with inhibitor than in inhibitor-free patients (P= <.01). Basal TGA parameters (ETP, peak thrombin height, and time to peak values were significantly better in hemophilic patients without inhibitor than in those with inhibitor (P= <.01). No difference was found between the first hour and 24th hour TGA parameter values between hemophilic patients without/with inhibitor after factor therapy. TGA lag time values measured 24 hours post-event were significantly shorter in rFVIIa than aPCC treatment in hemophilic patients with inhibitor (P=.04). First hour ETP and first hour and 24 hour peak thrombin height were significantly higher in aPCC than rFVIIa treatment in hemophilic patients with inhibitor (P=.01). First hour TEG parameter (R, K and alpha angle degree) values were found significantly in aPCC (12 episodes)than rFVIIa treatment (7 episodes) (P=.03). First hour and 24th hour INR values were significantly shorter in rFVIIa than aPCC (P= <.01). No association was found between first hour clinical responses and TGA parameters after inhibitor bypassing agent treatment. In this study, before and after bleeding episode treatment/surgery prophylaxis, basal, 1st and 2–24th hours lag time values of inhibitor-positive patients were significantly smaller than inhibitor-negative patients. Basal TGA parameters such as ETP, peak thrombin height, and time to peak thrombin values of hemophilic patients without inhibitor were significantly better than those of hemophilic patients with inhibitor. When hemophilic patients with or without inhibitor were evaluated for accurate clinic responses at 24 hours after factor replacement treatment, the clinical response was significantly better in the inhibitor-negative group. As a conclusion, for monitoring hemostasis in inhibitor patients related severe bleeding and major operations, TGA test may be used for most rational using of by-passing therapies.

Disclosures:
Kavakli: NovoNordisk: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Baxter: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau.