Low thrombin generation during major orthopaedic surgery fails to predict the bleeding risk in inhibitor patients treated with bypassing agents

Global Hemostatic Methods to Tailor Treatment With Bypassing Agents in Hemophilia A With Inhibitors- A Single-Center, Pilot Study

For patients with hemophilia A and high-titer inhibitors treated with bypassing agents there are no reliable methods to assess treatment effect. We investigated the utility of global hemostatic methods in assessing treatment with bypassing agents (rFVIIa or activated prothrombin complex [aPCC]). All patients with hemophilia A and inhibitors followed at the Coagulation Unit or the Pediatric Coagulation Unit at Karolinska University Hospital aged 6 years and above were eligible for this noninterventional study. Baseline plasma samples were spiked with bypassing agents in increasing concentrations (aPCC 50 U/kg, 100 U/kg, 150 U/kg, and rFVIIa 90 μg/kg and 270 μg/kg) in vitro. For patients treated with factor concentrates or bypassing agents follow-up samples were collected (in vivo tests). The samples were analyzed using overall hemostatic potential (OHP), and calibrated automated thrombogram, Calibrated Automated Thrombogram (CAT). Nine patients with hemophilia A with inhibitors were included. Spiking with rFVIIa normalized the coagulation potential in 6/8 samples, in 3 only with high dose. Only one sample did not improve adequately after spiking with aPCC. The improvement in hemostasis was reliably shown by both CAT and OHP. The baseline potential was, however, more often measurable by OHP compared to CAT. Factor concentrate had been administered to 5 patients normalizing the hemostatic potential in vivo in 2 (without spiking). The hemostatic improvement induced by spiking with rFVIIa or aPCC is shown by OHP and CAT, but the results have to be evaluated in larger cohorts.

Thrombin generation for monitoring hemostatic therapy in hemophilia A: A narrative review

Patients with severe hemophilia A (HA) have an increased risk of spontaneous and trauma-related bleeding because of a congenital absence of factor VIII (FVIII). Most severe HA patients use prophylactic FVIII concentrate, the effect of which can be monitored with FVIII activity level measurement. However, FVIII activity level is less valuable in predicting the potential clinical bleeding risk. Some patients still experience breakthrough bleeds despite adequate FVIII trough levels, whereas others do not bleed with trough levels below threshold. This difference may be caused by inter-individual differences in pro- and anticoagulant factors, the so-called hemostatic balance. Thrombin generation assays (TGAs) measure the hemostatic balance as a whole. Thereby, the TGAs may be a better tool in the guidance and monitoring of treatment in HA patients. In addition, TGAs offer the opportunity to determine the response to bypassing agents and treatment with non-factor replacement therapy, in which FVIII activity assays are not suitable for monitoring. This review summarizes the current knowledge about monitoring different HA treatment modalities by TGA, as a single treatment option and when used in a concomitant fashion.

Perioperative laboratory monitoring in congenital haemophilia patients with inhibitors: a systematic literature review

: Although the use of clotting factor concentrates is the mainstay of haemophilia care, the development of inhibitors complicates disease management. Perioperative management of patients with inhibitors is therefore a challenge. A systematic literature review was performed to identify literature reporting on the perioperative monitoring and management of haemophilia. MEDLINE, Embase and Cochrane databases were searched from database inception to 26 March 2018. Recent congress proceedings were also searched. Titles and abstracts, then full texts, were screened for relevance by two reviewers. Quality of included studies was assessed using the Critical Appraisal Skills Programme checklist. Of the 2033 individual entries identified, 86 articles met the inclusion criteria. The identified studies were screened again to find articles reporting perioperative laboratory monitoring in patients with congenital haemophilia A or B, resulting in 24 articles undergoing data extraction. Routine perioperative assay monitoring practices were the most commonly reported (n = 20/24); thrombin generation assay was the least commonly reported (n = 2/24). Other monitoring practices described were factor VII and factor VIII coagulation activity (n = 8/24, n = 5/24, respectively), and thromboelastography or rotational thromboelastometry assessments (n = 3/24). The impact of monitoring on treatment decisions was, however, rarely reported. In conclusion, many methods of perioperative monitoring of haemophilia patients with inhibitors have been identified in this review, yet there is a lack of reporting in larger scale cohort studies. More detailed reporting on the impact of monitoring outcomes on treatment decisions is also needed to share best practice, particularly as new therapeutic agents emerge.

Kaolin, used to trigger coagulation in thrombin generation test, increases sensitivity of the method in hemophilia patients

: Thrombin generation test (TGT) is well established tool to research blood coagulation in plasma of hemophilia patients. Traditionally coagulation in this test is triggered by a tissue factor (TF), an extrinsic coagulation pathway activator. However, it is known that disorders of the intrinsic pathway are most important for coagulation in hemophilia. In this study, we hypothesized that triggering coagulation via the intrinsic pathway could increase a sensitivity of the TGT to monitor hemophilia treatment. The aim of this study was to compare thrombin generation in hemophilia A patients with inhibitors to factor VIII before and after infusion of bypassing agent [recombinant-activated factor VIIa (rVIIa)] using standard activation of coagulation by TF or by kaolin, an activator of coagulation by intrinsic pathway. Endogenous thrombin potential (ETP) in nine patients was measured. ETP before (ETP0) and 60 min after rVIIa infusion (ETP60) were compared. It was shown that ETP0 and ETP60 were significantly different when using any coagulation activator (paired Student's t test, P = 0.017 and 3.7 × 10 for clotting activation by TF and kaolin, respectively). The ratios of ETP60/ETP0 were 1.2 ± 0.2 or 30.0 ± 22.4 (mean ± SD, n = 9) for coagulation activated by TF or kaolin, respectively, and were significantly different (paired Student's t test, P < 0.005). The TGT clearly distinguished between ETP0 and ETP60 in the case of any coagulation activator, but ETP increasing after rVIIa infusion was significantly higher when activated with kaolin. This provided increased sensitivity of this method for monitoring hemophilia therapy.

Over two decades of orthopaedic surgery in patients with inhibitors-Quantifying the complication of bleeding

Patients with haemophilia who have developed inhibitors against factor VIII (FVIII) or factor IX present a significant concern to those surgeons who operate on them. The evidence base for bypassing agents such as recombinant factor VIIa and activated prothrombin complex concentrate has amassed over several decades. The literature is open to positive interpretation on the successful use of these agents in the treatment of inhibitor-positive patients. However, there are equally persistent concerns amongst surgeons, in particular orthopaedic surgeons, regarding the high complication rate of bleeding. To explore and quantify this concern, we present a literature review spanning two decades of publications on haemophilia patients with inhibitors undergoing orthopaedic surgery. Irrespective of the progress made with haemostatic protocols, trepidation on embarking on surgery is valid. The high risk of bleeding is a function of the inherent complexity of the disease and rightfully translates into difficulties in its management. Combined with the prospect of orthopaedic surgery, those involved in the care of such patients are justified in their continued anxiety and diligence when considering the benefits in quality of life against the prevalent complications.

Combination of hemostatic therapies for treatment of patients with hemophilia A and inhibitors

BACKGROUND

Therapy application and monitoring of patients with hemophilia A (HA) and inhibitors are challenging. In the current study, combined FVIII - bypass therapy was implemented for a cohort of severe HA patients with inhibitors.

METHODS

Plasma of 15 HA patients with inhibitors was spiked ex vivo with FVIII, rFVIIa, FEIBA and their combinations and thrombin generation (TG) was studied. Some patients who experienced hemarthroses or required minor surgeries were treated by a combined concomitant administration of FVIII+FEIBA as IV bolus doses.

RESULTS

TG spiking studies showed individual responses not correlated to inhibitor titer. Combinations of agents augmented TG as compared to any single agent, while combined FVIII+FEIBA yielded the highest TG, supporting it as a potential treatment. Following emergent successful surgery of child treated by concomitant FVIII+FEIBA, a total of 396 episodes in 7/15 patients were treated with concomitant FVIII+FEIBA. Five patients were treated for bleeding episodes only, whereas 2 were children undergoing immune tolerance induction (ITI) with FEIBA prophylaxis. Four minor surgeries were performed on FVIII+FEIBA repeated infusions. Neither thrombosis nor any other adverse events were documented.

CONCLUSION

A combination of FVIII+FEIBA may be effective and safe as an alternative treatment option for some high-responding inhibitor patients.

Global clotting assays - monitoring the effect of by-passing agents in haemophilia patients with inhibitors

The development of FVIII/FIX inhibitor alloantibodies represents a severe complication requiring specific laboratory evaluation for establishing a life-saving therapy regimen. Our preliminary study aimed at elaborating a laboratory strategy for monitoring the effectiveness of Activated Prothrombin Complex Concentrate (APCC) and recombinant activated factor VII (rFVIIa) in haemophiliacs with inhibitors, by checking the reliability and clinical value of three complementary assays: clotting-time based coagulometry, thrombelastography (TEG) and thrombin generation assay (TGA). The investigations were performed on 7 patients with severe haemophilia A with high titer inhibitors treated for 12 episodes of severe bleedings, 5 of them for surgical interventions. After the administration of bypassing agents (BPAs) the clotting-time based assay brought changes only on prothrombin (p<0.01), potentially signaling a thrombotic risk, without any impact on the global hemostasis. TEG displayed prompt significant improvement only after rFVIIa (90μg/kg). TGA revealed significantly improved values for peak and velocity index, time to peak and start tail after both BPAs. Despite some disparities between biological hemostatic phenotype and clinical response to therapy, we concluded that TEG and TGA are the only current exploratory assays, expressing the quality of haemostatic control, representing a real support for a personalized, adapted therapy in hemophilia with inhibitors.