Poor correlation between aPTT, anti-Xa levels and heparin dose in children receiving therapeutic doses of unfractionated heparin

Abstract number: P0060

Kuhle S., Eulmeskian P., Massicotte M. P., Vegh P., Persaud K., Kavanagh B., Mitchell L.

The Hospital for Sick Children, Canada

Background  

Unfractionated heparin (UFH) is required in a large number of children for the prevention and treatment of thromboembolic events (TE) in high risk situations. Adequate monitoring of UFH therapy is essential to minimize risk of bleeding and thrombotic complications. There are data suggesting that the activated partial thromboplastin time (aPTT) and anti-Xa activity that are used for monitoring UFH therapy in adults are not optimal in children.

Objective  

To investigate the correlation of aPTT, anti-Xa levels and UFH dose in children receiving therapeutic doses (target anti-Xa level 0.35–0.70 U mL^-1).

Design/methods  

Prospective cohort study performed in a single-center. Non-selected consecutive children (>36 weeks-18 years) treated at the Hospital for Sick Children, receiving UFH for a minimum of 24 h. The aPTT (Haemoliance Thrombosil, Beckman Coulter assayed on a MLA 1400) and anti-Xa activity (Haemoliance Anti-Xa chromogenic kit, Beckman Coulter assayed on MLA 1400) results from routine coagulation monitoring were collected prospectively.

Results  

During the first 4 months of this ongoing study, 20 patients (median age 2 months, range 1 week to 15 years) were enrolled. Underlying disorders in the patients were congenital heart disease (n = 13), pulmonary embolism (n = 2), malformations (n = 2) and liver transplant (n = 1). Median UFH dose was 28 U hg^-1 h^-1 (4–50.4). A total of 188 paired aPTTs and anti-Xa levels were performed. There was little correlation between aPTT and anti-Xa levels (r² = 0.205) and APTT and UFH dose (r² = 0.19). There was no relationship between anti-Xa levels and UFH dose (r² = 0.00007) (Fig. 1).

Conclusions  

The aPTT and anti-Xa levels do not correlate with UFH dose in children receiving therapeutic doses of UFH. Currently available tests do not enable monitoring of UFH therapy.