Abstract Number: PB1312
Meeting: ISTH 2020 Congress
Background: Antithrombin (AT) is a natural anticoagulant inhibiting thrombin and factor Xa and thus accelerating the neutralisation of coagulation proteins. LMWH is responsible for accelerating AT interaction with thrombin and Xa. AT deficiency (acquired or congenital) reduces the ability to achieve the desired anticoagulant effect using LMWH. The anti-Xa test measures the activity of heparin/LMWH against the activity of activated coagulation factor X.
Aims: Determination of the Antithrombin activity levels having an effect on LMWH dosing in a paediatric cohort.
Methods: AT activity levels were prospectively measured (2y period) in patients < 1 y of age pre-operatively scheduled for LMWH post operatively (n= 335).
The cut-off AT activity level affecting Anti-Xa levels was determined by performing in vitro heparin recovery.
Anti-Xa assay type was evaluated; AT supplementation (AT+) and without (AT-) on heparin recovery (n=54).
Results: Patients (n=54) receiving LMWH therapy showed that the LMWH assay (AT+) had greater heparin recovery compared with the LMWH (AT-) assay. In vitro analysis showed that the heparin recovery was dependent on AT levels for both types of anti Xa assays. There was a clinically significant marked reduction in the amount of heparin recovered when AT activity levels fell below 60%. Heparin levels remained within the sub therapeutic range (0.25-0.5 IU/ml).
210/335 patients were found to have AT activity less than 0.60 IU/ml (mean 0.40 IU/ml) with the majority of patients (n= 209) < 1 month old. Mean AT activity levels of >0.60 IU/ml were found in patients > 1 month of age.
Conclusions: LMWH requires the presence of AT which may be limiting in determining anti-Xa levels in AT deficient patients. The cut-off concentration at which AT had an effect on Anti-Xa levels was 60%, in this study 210 patients had AT activity < 0.60 IU/ml. This finding has implications for LMWH dosing in neonates.
To cite this abstract in AMA style:Regan I, Pillion C, Riordan M, Nolan B. Antithrombin Activity Level below 60% in Children Has Implications for Heparin (LMWH) Dosing [abstract]. Res Pract Thromb Haemost. 2020; 4 (Suppl 1). https://abstracts.isth.org/abstract/antithrombin-activity-level-below-60-in-children-has-implications-for-heparin-lmwh-dosing/. Accessed May 6, 2021.
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