COAGULATION STUDIES


100 80 60 40 20 0


0 24 48 Time (hours) Time to therapeutic range: APTT versus anti-Xa.


of a single versus double spin and also the time limit after the specimens were collected. What we found was that the anti-Xa assay was easy and uncomplicated to use, and we had confidence in the results.”


He explained that transferring assay


protocol and calibrations was relatively straightforward and easy. Around three months were set aside to fully interface all the analysers and the assay into the hospital LIMS and to complete staff training. “To ensure a smooth transition, we made sure that are service users, from hospital clinicians to GPs, were kept fully informed of what was happening,” he added.


Rapid turnaround time Bhakta Buddhadev paid tribute to the way staff at all three hospitals set about implementing the change. “They understood exactly what was at stake and embraced the challenge and need to change very enthusiastically. Initial evaluation, agreeing workflow changes and training requirements were all carried out efficiently to ensure that nothing affected the smooth running of the laboratory.”


While Leicester still use the APTT


reagent for first-line routine screening, it has now moved to using anti-Xa for routine monitoring of LMWH and UFH treatment at all three sites. The team was keen to make the change due to the variable performance of APTT. Clinical colleagues had already started to use anti-Xa to set the baseline until dosage could be stabilised, and demand grew for an assay that could also deliver a rapid turnaround time. “We needed a heparin assay that could deliver a rapid TAT because at the


peak of COVID-19 admissions we were performing around 30 to 50 requests daily,” Mr Buddhadev added.


Guide to therapy Anti-Xa heparin monitoring represents an important test when faced with the multiple limitations on APTT. However, early adoption of anti-Xa was possibly hampered by the specialist nature of those early assays as well as the length of time to deliver a result. Fortunately, more recent


developments in assay technologies, such as Stago’s STA-Liquid Anti-Xa, make the test so robust that it can easily be part of the core coagulation laboratory repertoire, delivering results within six minutes. These innovations have made the test more cost-efficient. The same reagents are used for several assays, including DOACs, and this, combined with their long onboard stability, eliminates waste. Further, anti-Xa is proving to be a clinically important guide to therapy especially for the critically ill and for those undergoing complex surgical procedures. It provides a more direct measurement of UFH concentrations than APTT, with less variability and few interferences.


References 1 McLaughlin K, Rimsans J, Sylvester KW


et al. Evaluation of antifactor-Xa heparin assay and activated partial thromboplastin time values in patients on therapeutic continuous infusion unfractionated heparin therapy. Clin Appl Thromb Hemost. 2019; 25: 1076029619876030. doi: 10.1177/1076029619876030.


2 van Roessel S, Middeldorp S, Cheung YW, Zwinderman AH, de Pont AC. Accuracy


WWW.PATHOLOGYINPRACTICE.COM APRIL 2022


of aPTT monitoring in critically ill patients treated with unfractionated heparin. Neth J Med. 2014; 72 (6): 305–10.


3 Price EA, Jin J, Nguyen H, Krishnan G, Bowen R, Zehnder JL. Discordant aPTT and anti-Xa values and outcomes in hospitalized patients treated with intravenous unfractionated heparin. Ann Pharmacother 2013; 47 (2): 151-8. doi: 10.1345/aph.1R635.


4 Parker CR, Kataria V. Monitoring unfractionated heparin: A review of activated partial thromboplastin time versus antifactor Xa. AACN Adv Crit Care 2019; 30 (4): 305–12. doi: 10.4037/ aacnacc2019771.


5 Arachchillage DRJ, Kamani F, Deplano S, Banya W, Laffan M. Should we abandon the APTT for monitoring unfractionated heparin? Thromb Res 2017; 157: 157–61. doi: 10.1016/j.thromres.2017.07.006.


6 Marlar RA, Gausman J. The optimum number and types of plasma samples necessary for an accurate activated partial thromboplastin time-based heparin therapeutic range. Arch Pathol Lab Med 2013; 137 (1): 77–82. doi: 10.5858/ arpa.2011-0516-OA.


7 Guervil DJ, Rosenberg AF, Winterstein AG, Harris NS, Johns TE, Zumberg MS. Activated partial thromboplastin time versus antifactor Xa heparin assay in monitoring unfractionated heparin by continuous intravenous infusion. Ann Pharmacother 2011; 45 (7–8): 861–8. doi: 10.1345/aph.1Q161.


Further information is available from: Diagnostica Stago UK Theale Lakes Business Park 12 Moulden Way, Sulhamstead Reading RG7 4GB Tel: +44 (0)845 054 0614 Web: www.stago-uk.com


28 72


Outcome TTR (h)


Tests within TR


Tests performed per 24-h period


Dosage changes per 24-h period


Anti-Xa APTT


96


Major haemorrhage (n [%]) Mean LOS (days)


VTE/bleeding mortality (n [%])


APTT 48 (26) 42 (20)


2.8 (0.6) 1.6 (0.7) 6 (12)


25 (34) 3 (6)


Anti-Xa 28 (16) 66 (18)


2.5 (0.6) 0.8 (0.5) 5 (10)


17 (15) 1 (2)


P value <0.0001 <0.0001


<0.01 <0.0001 1


0.13 0.62


UFH monitoring using anti-Xa enables a faster time to therapeutic anticoagulation, higher numbers of tests with the TR, fewer tests and dosage changes, and potential LOS improvement (from Ref 7).


% achieve therapeutic anticoagulation


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