COAGULATION STUDIES
Change to anti-Xa from APTT in heparin monitoring: the clinical benefits
Recent developments in anti-Xa technology have resulted in a coagulation test that can easily be part of the core coagulation laboratory repertoire. Here, Stago compares and contrasts two methods for monitoring heparin therapy.
The arrival of COVID-19 has accelerated a trend in the NHS away from reliance on activated partial thromboplastin time (APTT) to assess a patient’s unfractionated heparin (UFH) concentration. The fundamental issue is that it may not accurately measure the amount of heparin present. Like all drugs, UFH must be administered in the right amount to ensure that its intended clinical effect is achieved, while avoiding adverse effects. The properties of the test used to monitor the therapeutic window can have a significant impact on the quality of care received by the patient.
As APTT is a non-specific surrogate
marker, it can only estimate heparin concentration. Many factors may influence the result, such as variations in potency of each batch of UFH and
differences between patient responses. These can vary even with the same patient at different times during the day. It is therefore possible to both underestimate and overestimate heparin levels with the APTT, risking both bleeding and thrombosis.1 Further, the recommended range
Activated partial thromboplastin time is a non-specific surrogate marker, and as such can only estimate heparin concentration
for APTT has never been determined on humans, only in animal studies, and a true concentration level never tested prospectively in humans.
In contrast, anti-Xa is a highly specific
assay, providing a more direct and therefore more accurate measurement of heparin activity, and so can offer an easy way of improving the care given to a patient.
Standardised anti-Xa assay The limitations of APTT came to the fore when monitoring critically ill COVID-19 patients who were suffering an intense inflammatory response. This was likely to induce many of the states known to interfere with APTT results, such as increased levels of coagulation factors and a disturbance to the overall haemostatic balance. If heparin dosage had to be monitored for these patients, then the need for a far more accurate test of their heparin concentration became paramount.2
When it was found that the virus
increased variation in the assay to unacceptable levels, laboratories were advised to use the more specific chromogenic anti-Xa assay, which is less susceptible to confounding factors. Further, many laboratories running anti- Xa can now provide round-the-clock heparin testing to satisfy urgent requests. Published clinical evidence is mounting that UFH monitoring with a standardised, fully automated anti- Xa assay such as Stago’s STA-Liquid Anti-Xa may be more appropriate for patients, especially those at high risk of bleeding.3,4
Studies that compare
Heparin is a copolymer of alternating glucosamine and uronic acid residues with heterogenous sulphation and acetylation patterns.
WWW.PATHOLOGYINPRACTICE.COM APRIL 2022
the monitoring of heparin infusion by both methods clearly demonstrate the benefits of anti-Xa.5
They show both
a reduced time to reach a therapeutic range, and how the patient remains
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