From Dr. David Floering:
Is anyone routinely using heparin anti-Xa assay to monitor heparin instead of PTT? If so, what are the experiences?
David Floering, MD
Medical Director, Pathology
Atrium Medical Center
Dr. Floering, thank you for your question. I have several acquaintances who have successfully converted from PTT to the chromogenic anti-Xa heparin assay for unfractionated heparin, low molecular weight heparin, and more recently, the synthetic pentasaccharide Fondaparinux. I’m forwarding your question to a few of them directly for comment. By hearsay, all have been quite happy with the better accuracy of the anti-Xa as it is unaffected by inflammation, raised factor levels, and inhibitors. I’ll await specifics from colleagues. Geo.
We converted some time ago at both Brooke Army Medical Cente
We converted some time ago at both Brooke Army Medical Center, and Wilford Hall Medical Center, two of the top military hospitals in the Department of Defense in San Antonio, TX. At those two institutions we use the hybrid curve. Also University Hospital, the large county hospital affiliated with the University of Texas Health Science Center in San Antonio has converted to monitoring all heparins with the anti-FXa assay. The only heparanoid not measured with the hybrid curve is fondaparinux. The biggest problem we have come across is with physicians still relying on the PTT assay and not trusting the anti-FXa results. This is despite the fact that there is a preponderance of literature that has cited the interference of anticoagulants, factor deficiencies, interfering substances, specimen collection, PTT reagent sensitivity and instrumentation affecting the PTT test. The only thing that may affect the anti-FXa assay is a low antithrombin level. Also, some physicians will try to monitor the patient with a PTT despite the result being elevated to start with when starting a subject on heparin. For example a recent case had test results of and INR of 2.6 with a PT of 26 seconds, a PTT of 200 seconds and a anti-FXa result of 0.4 units. The doctor stopped the heparin dosing. It was determined the subject had a lupus anticoagulant; the PTT was a false reading and the patient’s anti-FXa was at the low range of the therapeutic range (0.3-0.7). Therefore the patient was barely anticoagulated with heparin. Educating the physicians seems to be the primary problem with the conversion. Working closely with your pharmacy can assist the laboratory with this issue. Dave McGlasson
We have been using the anti-Xa for several years and have wi
We have been using the anti-Xa for several years and have within the last year switched to the hybrid curve to monitor both UFH and LMWH.
We have been considering making the switch since it would be
We have been considering making the switch since it would be a more accurate way of acessing the patent’s therapeutic status, however, it is no small task to change the practices of a large institution. I would be interested in hearing how the experiences of others have gone and if they feel that the effort and utilization was worth the work.