Does Hemoglobin S in Sickle Cell Trait and Sickle Cell Anemia Induce Higher Hemostatic Potential?

Introduction: Previous studies reported that patients with sickle cell disease (SCD) present with alterations of several factors involved in the coagulation system but also that global hemostatic potential parameters are enhanced in children with SCD suggesting hypercoagulability even at steady state. Such modifications have rarely been studied in adult SCD cohorts or individuals with a sickle cell trait (AS). On the other hand, observation of clinical events suggests that SCD adults patients are at higher risk of thrombosis, while those AS are at higher risk of deep venous and pulmonary thrombosis as well as sudden death after intense physical activity. The aim of our study was to characterise the global haemostatic potential of SS and AS adults.

Materials and Methods: Three groups were studied and consisted in 31 controls (group AA), 26 sickle cell trait (group AS) and 29 SCD patients (group SS) at steady state. Hemoglobin phenotype was assessed by combination of cation-exchange high performance chromatography (beta-thal short program BioRad) and capillary electrophoresis (Capillarys systems Sebia Benelux). We used the Calibrated Automated Thrombogram® to measure thrombin generation (TG) on platelet poor plasma (PPP) processed, aliquoted and frozen until needed for further testing in batches. TG was triggered using 1 pM tissue factor (TF) and 4µM phospholipids (PL) in two different conditions: with and without addition of thrombomodulin (TM). The interquartile range for several monitored parameters, namely lag time (min), time to peak (min), velocity index (nM/min), endogeneous thrombin potential (ETP, nM.min) and peak (nM) was compared between the 3 groups using Kruskall-Wallis and Dunn's multiple group comparison tests. Protein C activity (PC), free protein S (PS), factor VIII (FVIII), LDH, Thrombin anti-thrombin complex (TAT) and ultrasensitive CRP (CRP us) were also measured in parallel. Informed written consent was obtained from each subject prior to sampling; the study received approval from the local ethics committee.

Results: Without TM, there was a significant difference in peak, velocity index and lag time between the 3 groups (p<0.0001). Highest peak and velocity index, intermediate results and the lowest results were observed for SS, AS and AA groups, respectively. The lowest lag time was obtained for the SS group followed by the AS and AA groups (P< 0.0001).The addition of TM didn’t modify peak, velocity and lag time results. In contrast, ETP was higher for SS and AS group as compared with AA in the presence of TM (p<0.05). PC and PS were lower for the SS group as compared with AA group (p<0.01); PC was intermediate in the AS group. FVIII, CRP us, LDH and TAT were higher for SS as compared with AA (p<0.001).

Summary: In this preliminary study we showed that global hemostatic parameters were enhanced in adult SCD patients at steady state. This observation could be related to both a deficiency of the anticoagulant PC pathway and an inflammatory state. Even though we could not highlight hypercoagulability using individual parameters for AS individuals, they showed intermediate profile in global CAT test. In this later group, clinical impact should be investigated in a prospective way. Correlation with HbS level is currently ongoing.