From Maureen Tacke, Program Manager, Lab, Hematology/Coagulation, St. Luke’s Health System: Our institution is working towards a conversion to Anti-Xa monitoring for patients on UFH, however, our pharmacy group has a question. What are other facilities doing if a patient presents, needs UFH, and is already on a DOAC (the baseline anti-Xa or PTT is elevated)?
Thank you Maureen, I reached out to Lawrence Williams, MD, my University of Alabama at Birmingham colleague now moved to Mayo in Scottsdale. His response:
George, If a patient comes in on an anti-Xa DOAC, the anti-Xa (calibrated for heparin) test is exquisitely sensitive and you will be unable to use it if starting the patient on UFH. In such cases, we use the PTT to monitor heparin therapy for the first 48 hours of admission. To do so, we had to re-establish our PTT therapeutic range for heparin. This gives time for the effect of the DOAC to wear off, even for patients with poor renal function. Best, Lance.
In addition, X. Long Zheng, M.D., Ph.D., Division Director of Laboratory Medicine, UAB provided the attached reference. Conway SE, Hwang AY, Ponte CD, Gums JG. Laboratory and Clinical Monitoring of Direct Acting Oral Anticoagulants: What Clinicians Need to Know. Pharmacotherapy 2017;37:236-48. Best, Long.
Further, here is a 11-8-19 MedScape editorial, Stiles S. Simple Way to Stop, Restart DOACs for Surgery in Patients With Atrial Fib.
There is some interesting
There is a case study by Milito C, et al involving the chromogenic factor X (CFX) assay (not to be confused with the chromogenic anti-Xa heparin assay) that was published in Laboratory Medicine 2019. The case described persistent rivaroxaban effect due to in paired renal clearance and medications effects. They measured the CFX levels to determine DOAC effect and documented an on-treatment result of 22% rising to 78% after the DOAC was discontinued.
CFX results of 22–35% correlate to INRs of 2.0–3.5. CFX may be useful in the management of warfarin patients with lupus inhibitors or other interfering substances. It also may be used when the conventional PT/INR testing may not be suitable. CFX is also a valuable tool when subjects are transitioned from a direct thrombin inhibitor to warfarin. It is RUO currently for use with DOACs.
This Case Report was presented in Lab Med 2019 July Epub ahead of print.
Thank you very kindly for
Thank you very kindly for these responses. It is great to know how other facilities are handling these complexities.