Anti‐activated factor II assay for monitoring unfractionated heparin in children: results of the HEARTCAT study

Background Unfractionated heparin (UFH) is used for prophylaxis and treatment of thrombosis in children. Laboratory monitoring of UFH is needed to prevent over- or under-anticoagulation. Objectives Study objectives were to investigate i) the association between UFH dose and UFH effect as monitored by anti-IIa, ii) the relationship of anti-IIa and anti-Xa effects, and iii) the influence of patients’ age and other factors on UFH effect. Patients and methods Randomized controlled trial in children during cardiac catheterization, comparing high-dose UFH (100 units/kg bolus) versus low-dose UFH (50 units/kg bolus). Blood samples were drawn at baseline, after 30, 60 and 90 minutes. For the purpose of this study, 49 children and 117 blood samples were evaluated. Results The anti-IIa assay discriminated well between high and low-dose UFH. Multiple regression demonstrated a significant influence of UFH dose and age on anti-IIa levels. Younger children had lower anti-IIa levels than older children, an effect more pronounced at low-dose UFH. Anti-Xa/anti-IIa ratios were equal at low-dose UFH. However, anti-Xa levels were relatively increased over anti-IIa in infants and after high-dose UFH bolus. Conclusion The UFH effect on anti-IIa levels is lower in infants compared to older children. This influence of age appears to be dose-dependent, more pronounced at low-dose UFH. Anti-Xa versus anti-IIa levels are not equal, particularly in infants and after high dose UFH. Monitoring UFH using solely anti-Xa assays may not be sufficient in children and the anti-IIa assay may provide important complementary information. This article is protected by copyright. All rights reserved.