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The impact of age upon therapeutic response to unfractionated heparin (UFH) in children is proposed to reflect quantitative and potentially qualitative differences in coagulation proteins across childhood. This study explores the UFH-dependent tissue factor pathway inhibitor (TFPI) release in children compared to previously published data in adults. Children <16 years of age undergoing cardiac angiography formed the population for this prospective cohort study. TFPI release was measured prior to (baseline) and at 15, 30, 45 and 120 min post-UFH dose. This study demonstrated that, whilst the immediate release of TFPI post-UFH was similar in children compared to adults, TFPI release in children remained increased and consistent for a significantly longer period post-UFH administration compared to adults. Plasma TFPI levels in children did not demonstrate an UFH concentration -dependent reduction, as has been previously reported in adults. The prolonged TFPI-mediated anticoagulant levels observed in children administered UFH may contribute to the increased rate of major bleeding reported in children compared to adults. Furthermore, we postulate that this sustained UFH-dependent increase in TFPI levels in children may influence the binding of UFH to competitive plasma proteins, such as those involved in the immunological response to UFH associated with heparin-induced thrombocytopenia. [ABSTRACT FROM AUTHOR]

Paediatric recommendations for unfractionated heparin (UFH) management are extrapolated from adult trials, a practice that may contribute to the inferior UFH-related outcomes in children compared to adults. This is the first study to determine UFH concentration in a population of children and correlated UFH concentration with measures of UFH effect. Correlation coefficients between protamine titration (concentration) and activated partial thromboplastin time (APTT), anti- activated factor X (Xa) assay and thrombin clotting time (effect) were 0·59, 0·46 and 0·52 respectively. A protamine titration level of 0·2–0·4 iu/ml in children was not equivalent to an anti-Xa assay of 0·35–0·7 iu/ml but to an anti-Xa assay 0·17–0·85 iu/ml. In addition, use of the anti-Xa or protamine titration assays to establish an APTT therapeutic range resulted in upper limits of APTT ranges exceeding 200 s. Existing methods for determining therapeutic ranges for UFH in adult populations do not produce equivalent ranges in children. As a result, paediatric clinical guidelines that state a therapeutic range for UFH can be determined using a protamine titration assay of 0·2–0·4 iu/ml or an anti-Xa assay of 0·35–0·7 iu/ml are not based on appropriate evidence. There is an urgent need for change in our approach to the use of UFH in children. [ABSTRACT FROM AUTHOR]

Abstract: Introduction: Anti-Factor Xa (Anti-Xa) assays specifically determine the anticoagulant activity of UFH by measuring the ability of heparin-bound Antithrombin (AT) to inhibit a single enzyme, Factor Xa (FXa). Recent improvements in the automation, cost-effectiveness and accessibility of the assay to clinicians, have resulted in the Anti-Xa assay becoming a part of daily clinical practice in many institutions. Objectives: We hypothesized that different Anti-Xa assays have different applicability for use in clinical settings, depending on the amount of UFH administered. This was investigated in a tertiary paediatric institution. Materials and methods: Samples were collected from children receiving Low-dose of UFH of at least 10 IU/kg/h, with or without a previous bolus of up to 25 IU/kg/h, within the previous 6 h in the PICU and HDU. High-dose UFH population consisted of children undergoing Cardiac Catheterization (CC), who received a bolus of UFH of 100 IU/kg body weight, 30 min prior to sampling. Results and conclusions: The Anti-Xa activity for a given dose of UFH was found to vary significantly based on the Anti-Xa assay and the population being monitored. Our study suggests that the MODIFIED COMATIC Anti-Xa assay provides the best physiological measure of the UFH effect in children, as it does not introduce sources of error, such as exogenous AT, which may increase the measured ant Factor Xa activity, nor Dextran Sulphate which can displace plasma protein bound heparin and once again leading to falsely elevated assay results. Further studies that include assessment of clinical outcomes are required to confirm the applicability of use of this particular assay in monitoring UFH therapy. [Copyright &y& Elsevier]