Thrombin Generation in Severe Hemophiliacs with Different Clinical Phenotype.
Authors: Santagostino Elena , Mancuso Maria E. , Tripodi Armando , Chantarangkul Veena , Clerici Marigrazia , Sei Cinzia , Mannucci Pier M. 
Published: April 2020

Abstract
Introduction: based on the plasma levels of factor VIII or IX (FVIII, FIX) hemophiliacs usually experience bleeding episodes of different clinical relevance. Some hemophiliacs classified as severe, having undetectable coagulant activity of FVIII or FIX (FVIII/FIX:C &lt;1 U/dL), exhibit a mild bleeding tendency, but the basis for this heterogeneous clinical expression of the disease is still poorly understood. The thrombin generation measured as endogenous thrombin potential (ETP) in patients with hemophilia A has shown a significant correlation with FVIII levels while a wide range of ETP values were found in patients with FVIII:C &lt;1 U/dL (Chantarangkul et al. Haematologica88: 547–54, 2003) suggesting the potential for distinguishing different coagulation profiles among severe hemophiliacs.
Objectives: this case-control study was designed to investigate the relationship between ETP values and clinical phenotype in severe hemophiliacs, in order to evaluate the use of this measurement as an indicator of the bleeding tendency. The impact of thrombophilic mutations PTG20210A and FV Leiden into the modulation of the hemophilia phenotype was also evaluated. Patients: severe hemophiliacs (FVIII/FIX:C &lt; 1 IU/dL) older than 18 years, without a history of inhibitors and treated on demand were eligible. Two groups of patients with severe hemophilia, representing the extremes of the clinical spectrum of bleeding symptoms, were defined. Patients with extremely mild bleeding diathesis (mild bleeders, MB) should have had 2 or less spontaneous bleeding episodes per year; a concentrate consumption lower than 120 U/Kg/year; a total radiological score ≤ 10 points and a total orthopaedic score ≤ 4 points (scoring system recommended by the Orthopaedic Advisory Committee of the World Federation of Hemophilia). Patients with markedly severe bleeding history (severe bleeders, SB) should have had 25 or more spontaneous bleeding episodes per year; a concentrate consumption greater than 3000 U/Kg/year; a total radiological score ≥ 40 points and a total orthopaedic score ≥ 25 points. Patients who did not fit the definition criteria of neither MB nor SB were considered as “intermediate” bleeders (IB).
Methods: plasma samples were obtained after a minimum wash-out period of 5 days. FVIII levels were measured by chromogenic assay. ETP was measured in platelet-rich plasma after addition of tissue factor.
Results: 22 MB, 22 SB and 28 IB were enrolled. No statistically significant differences were found in the age of patients included in the three groups (median: 32, 38 and 38 years). PTG20210A was detected in 5% MB and 4% IB; FV Leiden in 7% IB and 5% SB. ETP values were significantly higher in MB (median: 850 nM) compared with both IB (median: 478 nM; p&lt;0.05) and SB (median: 414 nM; p&lt;0.05). Also p for trend was statistically significant (p&lt;0.05).
Conclusions: this study shows that thrombin generation measurements may allow to identify patients with mild bleeding diathesis among severe hemophiliacs, in contrast with the features of conventional functional assays. On this basis, ETP measurement in the setting of severe hemophilia may be useful to improve the selection of candidates for early prophylaxis.