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Thrombin regulation in children differs from adults in the absence and presence of heparin
1Department of Pediatrics, McMaster University Medical Centre, Hamilton, Ontario, Canada.
Insights
Children exhibit distinct thrombin regulation compared to adults, potentially offering protection against blood clots. This difference may necessitate adjusted heparin therapy for pediatric deep vein thrombosis (DVT).
Area of Science:
- Pediatric Thrombosis and Hemostasis
- Coagulation Physiology
- Thrombin Regulation Mechanisms
Background:
- Physiologic protective mechanisms against thromboembolic complications in children remain largely unknown.
- Thrombin plays a central role in thrombosis, making its regulation a key area of investigation.
- Current deep vein thrombosis (DVT) treatment in children often relies on adult-derived heparin therapy guidelines.
Purpose of the Study:
- To investigate and compare thrombin generation and regulation in pediatric and adult plasma.
- To elucidate potential age-related differences in coagulation that may influence thromboembolic risk.
- To assess the impact of varying heparin concentrations on thrombin generation in children versus adults.
Main Methods:
- In vitro chromogenic assays were used to measure thrombin generation capacity in plasma samples from children (1-16 years) and adults (20-45 years).
- Prothrombin addition experiments were conducted to assess its role in pediatric thrombin generation.
- Inhibition assays measured the capacity of plasma to inhibit alpha-thrombin, with subsequent analysis of thrombin complexed to alpha 2-macroglobulin (alpha 2M).
- The effect of different heparin concentrations (0.1, 0.2, and 0.4 U/ml) on thrombin generation was evaluated in both pediatric and adult plasmas, with antithrombin III (ATIII) involvement assessed.
Main Results:
- Pediatric plasma demonstrated a 26% lower capacity for thrombin generation compared to adult plasma (p < 0.001).
- Supplementation with purified prothrombin normalized thrombin generation in pediatric plasma to adult levels.
- Children's plasma showed a 21% higher capacity to inhibit alpha-thrombin (p = 0.020), with increased thrombin complexation to alpha 2M.
- At low heparin concentrations, thrombin generation was significantly reduced by 30% in children compared to adults (p < 0.001).
- Antithrombin III effectively inhibited thrombin in both groups at therapeutic heparin levels.
Conclusions:
- Thrombin regulation in children differs significantly from adults, characterized by reduced generation and enhanced inhibition.
- These distinct coagulation profiles may contribute to a natural protection against thromboembolic events in pediatric populations.
- The observed differences suggest that current heparin dosing protocols for DVT in children may require re-evaluation and potential adjustment based on age-specific hemostatic function.
Abstract:
The physiologic mechanisms that protect children from thromboembolic complications are not known. We investigated the regulation of thrombin in children because of its central importance to thrombosis. The capacity to generate thrombin in vitro (chromogenic assay) was decreased by 26% in plasmas from children (1-16 yrs; n = 102) compared to adults ([20-45 yrs; n = 20; p < 0.001]). The addition of purified prothrombin to plasmas from children increased thrombin generation to adult values. The capacity of plasmas to inhibit 125I-alpha-thrombin was increased by 21% in children compared to adults (p = 0.020), with significantly more thrombin complexed to alpha 2-macroglobulin (alpha 2M) in children. When DVT occur in children, adult guidelines for heparin therapy are used. At low heparin concentrations (0.1 and 0.2 U/ml), thrombin generation was decreased by 30% in children compared to adults (p < 0.001). At high heparin levels (0.4 U/ml), thrombin generation was negligible in all plasmas. ATIII inhibited over 95% of thrombin in all plasmas in the presence of heparin. In summary, thrombin regulation differs in children from adults and may protect children from thromboembolic complications. When DVT do occur, heparin requirements may differ in children compared to adults.