Global Coagulation Assays in the Normal Population: Female Gender, Older Age and East Asian Ethnicity Associated with Prothrombotic Parameters

Aim

Thrombotic diseases are major causes of morbidity and mortality, and yet there are currently no laboratory tests to evaluate this risk. Global coagulation assays such as thrombin generation via calibrated automated thrombogram (CAT) and thromboelastography (TEG), may be better surrogate measures of an individualÕs thrombosis risk. However, the evaluation of age, race and gender differences in the normal population is important prior to the inclusion of these assays into studies on diseased populations.

Methods

Normal controls with no thrombotic history and no anticoagulant/antiplatelet use were recruited. Routine tests were performed to exclude underlying risk factors including full blood count, thrombophilia screen and fasting lipids. All samples were citrated; platelet poor plasma (PPP) samples were double-centrifuged at 2500G, aliquoted and frozen at -80^o C within 2 hours of collection. TEG 5000S analysis was performed within 4 hours of collection, using whole citrated blood under standard manufacturer guidelines. CAT was performed with PPP using standard commercially available (STAGO) 5 pmol reagent and flurogenic (Fluca-Kit).

Results

63 normal controls (43F, 20M) with median age of 36.5 (20-75) years were recruited. None had abnormal platelet or coagulation parameters.

TEG: 36 volunteers (57%) had TEG parameters outside the manufacturerÕs normal range. Females and older individuals (age >50 years) had more prothrombotic TEG parameters including increased maximum amplitude (MA), alpha-angle and derived thrombin generation; with reduced R and K time. Older females (age >50 years) also had more prothrombotic parameters compared to younger females. Clot lysis (LY30) was significantly lower in the older population with no gender differences. (Table 1)

CAT: Females had higher endogenous thrombin potential (ETP), which represented the total thrombin formed, and higher velocity index. Older individuals had higher ETP but paradoxically a longer lag time. (Table 1)

CAT vs TEG: There was no correlation between TEG parameters (such as MA or derived thrombin generation), and ETP via CAT (r²=0.005 and r²=0.006 respectively).

Race differences: Of the 63 volunteers, 25 and 30 were of European and East Asian origin respectively. East Asians had significantly higher ETP, thrombin peak and velocity index (p<0.01), but these differences were less apparent using TEG, which also evaluated the platelet effect on clot formation. Statistically significant variation was only seen in the α-angle (p=0.04). (Table 2)

Conclusion

This study demonstrates that there are significant gender and age differences within the normal population. 57% of our volunteers had at least one TEG parameter outside the manufacturers reference range. Females had more prothrombotic parameters, which was independent of hormonal status. Older individuals (age >50 years) having more prothrombotic parameters, particularly clot lysis (LY30) using TEG, suggests a role of fibrinolysis in the futher evaluation of thrombotic risk. East Asians had significantly lower CAT parameters, which may explain the lower venous thrombotic risk seen in this population. Our results suggest that a localized reference range, tailored to gender, age and ethnicity is required for global coagulation assays.