Replacing the aPTT for monitoring of unfractionated heparin with the Prothrombinase induced Clotting Time (PiCT) – significant influence on dosing.

W. Korte, L. Graf, C. Knöpfel (1St. Gallen, Switzerland)

Laboratory tests
Date: 17.02.2017,
Time: 17:15 - 18:15

Objective: We recently showed in a prospective multicentre trial that the Prothrombinase induced clotting time (PiCT) is a more reliable tool than the aPTT for unfractionated heparin (UFH) monitoring (Brisset et al., JTH 2016), suggesting that its use might also influence and improve the clinical course of UFH therapy. Compared to chromogenic anti-Xa-assays, PiCT has all the advantages of a clotting based assay, but is predominantly sensitive to F. X and F. II inhibition at the same time. After implementing PiCT for routine UFH monitoring, we therefore investigated whether replacing aPTT with PiCT for UFH monitoring was associated with changes in UFH dosing. Rules to be used for UFH monitoring with both, initially aPTT and later PiCT were based on target anti-Xa levels; rules were not changed with the implementation of PiCT monitoring, unless mandated by the clinical course.

Methods: We retrospectively compared patients treated with UFH before implementation of PiCT monitoring and thereafter in various departments (internal medicine, neurology and surgery departments, including the respective intensive and critical care units); we compared the daily doses of UFH used as documented in the patient charts. Data were not adjudicated. Data were compared by Mann-Whitney testing for independent samples.

Results: Until now, a total of 439 aPTT measurements and 625 PiCT measurements were identified. Median UFH doses documented were 27'000 U / day with aPTT monitoring (IQR 20'000 – 29'500) and 25'000 U / day with PiCT monitoring (IQR 20'000 – 27'000), indicating a significant difference (p = 0.035).

Conclusion: In this first comparison of aPTT and PiCT for routine UFH monitoring outside of a prospective trial, PiCT monitoring was associated with a significantly reduced daily dose of UFH. This suggests that UFH monitoring by PiCT not only is analytically more precise (Brisset et al., JTH 2016), but it also suggests that PiCT allows more precise dosing. More research is needed to confirm these findings and to identify other variables possibly indicating a potential change in outcome when using PiCT instead of aPTT for UFH monitoring.