The plasma hemostatic proteome: thrombin generation in healthy individuals

Abstract

Background and objectives: The range of plasma concentrations of hemostatic analytes in the population is wide. In this study these components of blood coagulation phenotype are integrated in an attempt to predict clinical risk.

Methods: We modeled tissue factor (TF)-induced thrombin generation in the control population (N = 473) from the Leiden Thrombophilia Study utilizing a numerical simulation model. Hypothetical thrombin generation curves were established by modeling pro- and anticoagulant factor levels for each individual. These curves were evaluated using parameters which describe the initiation, propagation and termination phases of thrombin generation, i.e. time to 10 nm thrombin (approximate clot time), total thrombin and the maximum rates and levels of thrombin generated.

Results and conclusions: The time to 10 nm thrombin varied over a 3-fold range (2.9-9.5 min), maximum levels varied over a approximately 4-fold range (200-800 nm), maximum rates varied approximately 4.8-fold (90-435 nm min(-1)) and total thrombin varied approximately 4.5-fold (39-177 microm s(-1)) within this control population. Thrombin generation curves, defined by the clotting factor concentrations, were distinguished by sex, age, alcohol consumption, body mass index (BMI) and oral contraceptive (OC) use (OC > sex > BMI > age). Our results show that the capacity for thrombin generation in response to a TF challenge may represent a method to identify an individual's propensity for developing thrombosis.

Figures

Fig. 1

Thrombin profiles of healthy individuals. (A) Factor levels from 473 healthy individuals were input into Clot Speed II and initiated with a 5-pm stimulus of tissue factor and solved for active thrombin over a 20-min time frame (same as whole blood assays). The mean simulation with the standard deviation (294 ± 136 nm) at all the time points is shown as the center curve. A fast (7.6 ± 0.2 min and max. levels of 579 ± 49 nm thrombin) and slow (14.4 ± 0.7 min and a maximum level of 368 ± 41 nm thrombin) population (N = 13 per group) were separated out and compared with the average time it takes to reach maximum thrombin levels (10.6 ± 1.4 min). The inset panel shows the standard deviation of these populations. (B) Thrombin simulations for three individuals; a low-, mid- and high-thrombin generator. From left to right, the individual in the first curve had maximum thrombin levels of 778 nm, the second individual (middle curve) had maximum thrombin levels of 436 nm, and the last individual had maximum levels of 196 nm thrombin.

Fig. 2

Histograms of the thrombin parameters for the healthy population. Parameters that are used for pattern recognition are (A) time to 10 nm thrombin (min, estimated clot time); (B) maximum rate of thrombin generated (nm min−1); (C) maximum level of thrombin generated (nm); (D) total thrombin generated (μms, area under the curve).

Fig. 3

The influence on thrombin generation by potential risk factors. Numerical simulations were performed on the groups of individuals that fell within each risk factor category. Coagulation was initiated with a 5-pm stimulus of tissue factor and thrombin generation was followed for 20 min. The risk factors are: (A) Sex; women (n = 272) and men (n = 201); (B) age; minimum age 45 years (n = 250) and maximum age 45 years (n = 223); (C) body mass index (BMI) ≤26 kg m−2 (n = 275) and > 26 kg m−2 (n = 193); (D) oral contraceptives (OC); OC use (n = 54) and no OC use (n = 99). All thrombin generation curves are shown as the mean and 95% CI.