Thrombin Generation in Sickle Cell Disease: Insights From Computerized Automated Thrombography.

SCD is considered to be a hypercoagulable state. Because of the great complexity of the hemostatic system it has not been easy to establish an etiological link between hypercoagulability and SCD vascular pathology. In this study we evaluate hemostatic perturbations in adult SCD patients by employing the computerized automated thrombogram (CAT), a novel thrombin generation assay that provides a global measure of coagulation potential and a direct assessment of the coagulation phenotype (Hemker HC et al.,Thromb Haemost. 2006; 96:553–61). We aim to characterize the coagulation phenotype of the SCD patient by a panel of CAT assay parameters.

A total of 23 SCD patients (HbSS and HbSbeta⁰Thalassemia; 18 –58 years) were evaluated. Control group consisted of 6 age-matched controls (males=3, females=3). SCD plasma samples were obtained at baseline during routine clinic visits. Platelet poor plasma (PPP) ± corn trypsin inhibitor (CTI) - to minimize variability from activation of contact pathway during sample collection- was analyzed by CAT using 2 different triggers for initiation of thrombin generation: i) High trigger –5pM Tissue factor (TF) with 4uM phospholipid (PL) and ii) Low trigger- 1pM TF with 4uM PL. Five CAT assay parameters were studied – Lag time, Endogenous thrombin potential (ETP), Peak thrombin (Peak), Time to peak (ttPeak) and Start Tail. Students t-test was used to compare means of CAT assay parameters between SCD patients and controls.

Lactate dehydrogenase (a biomarker of hemolysis-associated nitric oxide resistance and endothelial dysfunction) correlated with CAT assay parameters including lagtime (r= −0.35, p=0.05); ttPeak (r=−0.45, p<0.02) and start tail (r=−0.47, p=0.01).

In this study interesting differences in kinetics of thrombin generation were noted between SCD patients and controls as follows: Thrombin generation with high trigger demonstrated a rapid burst of thrombin generation in SCD plasma (shorter lagtime, lesser ttpeak) vs. controls. Overall lower and less sustained thrombin generation (i.e. decreased ETP and early start tail) followed this rapid burst in SCD. Thrombin generation with low trigger also showed significantly decreased ttpeak of thrombin generation in SCD with similar overall lower thrombin generation and early start tail. ETP, Peak thrombin level, and ttPeak have shown correlations with clinical hypercoagulable states evaluated by the CAT assay. We speculate that this paradoxical upsurge of thrombin generation with swift attenuation suggests the presence of a compensatory upregulation of Tissue Factor Pathway Inhibitor (TFPI) or anticoagulant responses in SCD that results in rapid quenching of thrombin generation. Additionally, we have previously shown that heme, a product of intravascular hemolysis, upregulates endothelial TF (J Thromb Haemost. 2008; 12:2202–9). The observed relationship between increased LDH and evidence of rapid response of thrombin generation is in keeping with this result. These preliminary data support the use of the CAT assay in further detailed analyses of mechanisms of thrombin generation in SCD.

No relevant conflicts of interest to declare.