Anti-factor IIa (FIIa) heparin assay for patients on direct factor Xa (FXa) inhibitors

BACKGROUND

Direct factor Xa (FXa) inhibitors are increasingly prescribed for outpatients, and those transitioning to unfractionated heparin (UFH) for hospital admission are monitored via an anti-FXa assay. Because of assay interference, UFH results would often be critically elevated, confounding dosing.

OBJECTIVES

An anti-factor IIa (FIIa) UFH assay was evaluated for clinical use.

METHODS

The BIOPHEN ANTI-IIa (Aniara Diagnostica) assay and anti-FXa INNOVANCE Heparin assay (Siemens Healthcare Diagnostics Products GmbH) were compared on the Siemens BCS XP system. Samples included UFH controls and calibrators and specimens from patients transitioning from apixaban or rivaroxaban to UFH. Method comparison, linearity, recovery, precision, and interference by direct FXa inhibitors were evaluated. The effect of the BIOPHEN ANTI-IIa assay on the rate of critically high UFH results was retrospectively reviewed 4 months after implementation.

RESULTS

Accuracy studies using 0.24 and 0.50 IU/mL UFH yielded means and standard deviations of 0.26 ± 0.01 and 0.58 ± 0.01 IU/mL, respectively. Within-run and between-run coefficients of variation were 4.6% and 15.5% for the low control, and 1.8% and 10.6% for the high control. The method comparison slope was 0.9965 (r2  = 0.9468). The linear range was 0.1 to 1.3 IU/mL. The assay measured UFH in the presence of 192 ng/mL apixaban or 158 ng/mL rivaroxaban. Introduction of the assay for clinical use reduced the monthly percentage of critically high results from 9.4% to 3.8% for admitted heparinized patients who recently discontinued apixaban or rivaroxaban.

CONCLUSIONS

The BIOPHEN ANTI-IIa assay is suitable for patients transitioning off apixaban or rivaroxaban.

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

Essentials Unfractionated heparin has variable effects in children and therefore, monitoring is essential. A randomized controlled trial substudy investigating an anti-IIa assay in children was conducted. Anti-IIa values are lower in younger children, an effect more pronounced at low-dose heparin. Heparin effect on Xa and IIa is not equal, particularly in infants and after high-dose heparin.

SUMMARY

Background Unfractionated heparin (UFH) is used for the prophylaxis and treatment of thrombosis in children. Laboratory monitoring of UFH is needed to prevent over-anticoagulation or under-anticoagulation. Objectives To investigate the association between UFH dose and UFH effect as monitored with the anti-activated factor II (FIIa) assay, the relationship between anti-FIIa and anti-activated factor X (FXa) effects, and the influence of patient age and other factors on UFH effect. Patients and methods This was a randomized controlled trial in children during cardiac catheterization, comparing high-dose UFH (100 units kg-1 bolus) with low-dose UFH (50 units kg-1 bolus). Blood samples were drawn at baseline, and after 30 min, 60 min, and 90 min. For the purpose of this study, 49 children and 117 blood samples were evaluated. Results The anti-FIIa assay discriminated well between high-dose and low-dose UFH. Multiple regression demonstrated significant influences of UFH dose and age on anti-FIIa levels. Younger children had lower anti-FIIa levels than older children, an effect that was more pronounced with low-dose UFH. Anti-FXa/anti-FIIa ratios were equal with low-dose UFH. However, anti-FXa levels were relatively increased over anti-FIIa levels in infants and after high-dose UFH bolus administration. Conclusion The UFH effect on anti-FIIa levels is lower in infants than in older children. This influence of age appears to be dose-dependent, being more pronounced with low-dose UFH. Anti-FXa and anti-FIIa levels are not equal, particularly in infants and after high-dose UFH. Monitoring UFH solely with anti-FXa assays may not be sufficient in children, and the anti-FIIa assay may provide important complementary information.