Abstract Number: PB1073
Meeting: ISTH 2022 Congress
Background: Patients treated with unfractionated heparin (UFH) and Low molecular weight heparin (LMWH) may require monitoring of anti-Xa activity in order to ensure adequate anticoagulation has been achieved. The release of platelet factor 4 (PF-4) from platelets over time has a neutralising effect on anti-Xa activity, leading to falsely reduced results and potential over-anticoagulation.
Aims: To assess the stability of anti-Xa activity and APTTr of patients samples anticoagulated with UFH & Daltaparin (LMWH) to determine the maximum viability of such samples, for local validation.
Methods: Blood was taken from normal donors into Sodium Citrate tubes, these tubes were spiked with UFH and Daltaparin to achieve 0.5 iu/L and 1.0 iu/L anti-Xa activity. Whole blood was then aliquoted, centrifuged and analysed for APTTr & anti-Xa activity at one hour intervals over ten hours. Anti-Xa activity testing was performed using the Biophen heparin LRT Kit (Hyphen Biomed) with drug specific calibrators and the APTTr was performed using Actin FS (Siemens) on the CN-6000 analyser (Sysmex).
Results: APTTr results were stable up to 4 hours for UFH samples, declining more significantly where the APTTr was more elevated (figure 1). The APTTr of LWMH spiked samples were equivalent to baseline after 10 hours.
Anti –Xa activity results for UFH and LMWH at 0.5 IU/ml and 1.0 IU/mL concentration showed stability up to 8 hours. A spurious low result was recorded at 5 hours for UFH 1.0 iu/ml, figure 2 shows this outlier.
Conclusion(s): Spiking studies suggest that a 4 hour stability is recommended for determining APTTr on patients treated with UFH. This supports our local protocol.
Our data suggests that the anti-Xa activity for LMWH and UFH is stable for 8 hours in whole blood samples held at room temperature, therefore the local time window for acceptance of anti-Xa has been extended to 8 hours.
To cite this abstract in AMA style:Gajendra P, Wigley C, Foxton E. Anti-Xa and APTT stability in whole blood – a comparison of UFH & LMWH [abstract]. https://abstracts.isth.org/abstract/anti-xa-and-aptt-stability-in-whole-blood-a-comparison-of-ufh-lmwh/. Accessed September 27, 2022.
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