Retrospective cohort study comparing activated partial thromboplastin time versus anti-factor Xa activity nomograms for therapeutic unfractionated heparin monitoring in pediatrics

BACKGROUND

Unfractionated heparin (UFH) is widely used to treat thromboembolic disease, but monitoring in children is challenging. Both activated partial thromboplastin time (aPTT) and anti-factor Xa activity (anti-Xa) are utilized, but a comparison of dosing nomograms has not been reported in pediatrics.

OBJECTIVE

To compare the performance of aPTT and anti-Xa for UFH monitoring in pediatric patients.

DESIGN/METHODS

A retrospective cohort study was conducted in patients ≤ 21 years old treated with UFH at Johns Hopkins Hospital from January 2009 to May 2011. For monitoring, an aPTT nomogram was used for the initial 15 months, and an anti-Xa nomogram was used for the subsequent 12 months. Clinical characteristics, laboratory data and outcomes were analyzed.

RESULTS

Thirty-four patients were monitored with aPTT and 26 patients with anti-Xa. There was no significant difference in median time to therapeutic range (11.6 h aPTT, 95%CI = 6.0-17.0; 9.9 h anti-Xa, 95%CI = 7.3-20.7) or per cent of patients achieving therapeutic measurements at 24 (79% aPTT, 95%CI = 62-91; 73% anti-Xa, 95%CI = 52-88) and 48 h (88% aPTT, 95%CI = 73-97; 96% anti-Xa, 95%CI = 80-100). However, anti-Xa measurements were more frequently therapeutic than aPTT (74% [95%CI = 69-78] vs. 54% [95%CI = 50-59]). Variance between anti-Xa and aPTT measurements was high (R(2)  = 0.236). No significant difference was seen in bleeding incidence (9% aPTT, 95%CI = 2-24; 15% anti-Xa, 95%CI = 4-35).

CONCLUSION

The time to achieve therapeutic measures and bleeding outcomes were not significantly different between anti-Xa and aPTT nomograms. However, a small study size limits the power to detect clinically relevant differences. The results warrant larger prospective studies of UFH monitoring in children with thromboembolic disease.