Thrombin Generation Assay During Orthopaedic Surgery In Hemophilia A With and Without Inhibitors: Results From In Vivo Studies

Although surgery is considered the major haemostatic challenge in patients with hemophilia, laboratory monitoring is limited to the measurement of factor VIII (FVIII) levels in response to concentrate infusions and the global effect of replacement therapy on the activation and maintenance of coagulation activation has never been investigated. Moreover, in hemophilia complicated by inhibitors no routine coagulation monitoring is available to assess haemostasis during surgery in patients receiving by-passing agents (BPA; namely, recombinant activated FVII, rFVIIa and activated prothrombin complex concentrate, aPCC). Thrombin generation assay (TGA) may be used to monitor haemostatic treatment both in inhibitor and non-inhibitor patients with hemophilia. The aims of this study were to investigate if the use of TGA in the surgical setting is able to provide information on global coagulation activation during FVIII replacement therapy and if it is related to the haemostatic and clinical response after BPA therapy in patients with inhibitors.

Thrombin generation was assessed in vivo in platelet-rich (PRP) and platelet-poor (PPP) plasma with the addition of corn trypsin inhibitor (CTI) in 17 patients with severe hemophilia A (9 with high-responding inhibitors) aged 5-59 years (median: 39) undergoing orthopaedic surgery at a single center. Four main parameters of the thrombin generation curve were evaluated: lagtime, endogenous thrombin potential (ETP), peak and time-to-peak. TGA was assessed once daily prior and 30 minutes after concentrate administration (FVIII or BPA) starting from the first pre-operative infusion and for at least the 4 consecutive post-operative days. Peri- and post-operative FVIII and BPA dosing and regimens were established according to our practice irrespective of TGA results. In non-inhibitor patients, FVIII levels were measured on the same blood samples drawn for TGA.

In the group of 8 non-inhibitor patients TGA values increased after the first FVIII concentrate infusion (i.e. pre-operative bolus), however during the post-operative period, when FVIII trough levels were maintained above 50 IU/dL in all patients, TGA was scarcely sensitive to the significant variation observed in FVIII levels prior (median: 74 IU/dL) and after (median: 155 IU/dL; p<0.001) FVIII daily infusions. A correlation between TGA parameters and FVIII levels was observed only for ETP and peak measured in PPP+CTI. No bleeding complication was observed in non-inhibitor patients, therefore no correlation between laboratory measurements and clinical outcome could be done. In the group of 9 inhibitor patients TGA values always increased after BPA administration however the test was not able to distinguish different haemostatic responses with respect to the type of drug (either rFVIIa or aPCC), the dose used and/or the occurrence of bleeding complications (n=5). Moreover, a lack of haemostatic response was detected by TGA over the post-operative period irrespective of treatment adjustments in all inhibitor patients. The results obtained in inhibitor patients were consistent both in PRP and PPP, with or without CTI. Finally, in both inhibitor and non-inhibitor patients TGA values after drug administration (either BPA or FVIII concentrates) were far from reaching normal values obtained in 17 healthy male controls.

Our results indicate that TGA is not a suitable tool to monitor hemophilia treatment in the surgical setting. In fact, in non-inhibitor patients TGA was moderately sensitive to the haemostatic response to FVIII replacement therapy as compared to FVIII levels monitoring. On the other hand, in inhibitor patients TGA was not able to predict either the haemostatic response to different BPA and/or dosing regimens nor the risk of bleeding complications.

No relevant conflicts of interest to declare.