Analysis of Racial Disparity in Plasma of Healthy Volunteers Using Rotational Thromboelastometry Reveals Higher Prothrombotic Profile in African Americans

Racial differences in the incidence of arterial and venous thrombotic events are well established in literature, with a higher incidence noted in African Americans compared to Caucasians. Several studies have tried to explain this difference, by looking separately at chemical biomarkers, socioeconomic and clinical risk factors. Yet the exact reason behind this disparity remains unclear. At least one study of thrombin generation suggested that African ethnicity was associated with increased peak thrombin generation when compared to Caucasians. Rotational thromboelastometry is a visco-elastic methodology that offers a global assessment of hemostasis using either whole blood or plasma. We explored the racial differences in rotational thromboelastometry findings using plasma samples from healthy volunteers.

We studied a cohort of 9 otherwise healthy adult volunteers with no history of cardiovascular nor thromboembolic events, 5 African Americans and 4 Caucasians. After informed consent, we collected citrated whole blood samples and processed them within 3 hours of phlebotomy. Platelet free plasma, obtained after centrifugation of whole blood for 20 minutes, was kept frozen at -70°C, and then thawed at 37°C for 5 minutes prior to testing. Samples were re-calcified with star-tem^® reagent, and then the in-tem^® reagent was added. The latter contains an optimized concentration of ellagic acid and partial thromboplastin phospholipid from rabbit brain. Thromboelastometry parameters including Clot Formation Time, Alpha Angle, and Maximum Clot Firmness were determined. We then compared the data between the two study populations using parametric unpaired Student’s t-test.

Our results showed that the Clot Formation Time was higher in the plasma of Caucasians when compared to African Americans with a difference between means of 40.1 ± 4.4 seconds (p <.0001); the Alpha Angle was lower in Caucasians with a difference between means of 3.45 ± 0.3 degrees (p <.0001); and the Maximum Clot Firmness was lower in Caucasians with a difference between means of 9.75 ± 2 mm (p <.01). These findings demonstrated that the plasma of Caucasians took longer to reach the maximum firmness, and this maximum firmness was less than that reached in the plasma of African Americans. This reveals a significantly increased prothrombotic profile in the plasma of African Americans compared to Caucasians.

Despite the limited number of participants, the striking observed differences in the thromboelastometry parameters suggest that global assays may offer benefit in assessing thrombotic risks in disparate patient populations, as they incorporate multiple components of the hemostatic system. Higher numbers of subjects and assessment of both whole blood and plasma are indicated. We are currently in the process of expanding our cohort to confirm these preliminary results.