George and Dr. Louann Lawrence have been communicating with a patient through the ASCLS Consumer Web Forum who experienced a DVT and PE in 2014 and has been on Xarelto since then. Her physician routinely orders a D-dimer to assess the risk of a recurrence after discontinuing Xarelto. The patient stops Xarelto for 24 hours before specimen collection, but each time the D-dimer result is around 800 ng/mL, reference limit 240 ng/mL, so she resumes therapy. She has since had her D-dimer performed at another facility using an alternate technology, yielding a result of 230 ng/mL, within the reference interval. She subsequently had a D-dimer performed at a reference laboratory and the results are normal, yet her D-dimer remains elevated to approximately 800 ng/mL when measured at the original site. What could be causing this large difference?
Added April 16, 2016. George attended the Thrombosis and Hemostasis Summit of North America in Chicago, and was able to present this problem to several experts. Dean Willett of Instrumentation Laboratory, Inc sent a reference illustrating the various plasma components that may interfere differentially with the various D-dimer assays. Thay are lipemia, rheumatoid factor, hemolysis, human anti-mouse antibody, and parallel fibrin degradation products. Bob Gosselin, UC Davis, agrees, and confirms that Xarelto would be unlikely to associate with a raised D-dimer. All agreed this was a technique-specific interference issue.
For this patient, George recommended reflexing to a manual ELISA technique, the D-dimer reference technology, which may provide an opportunity to control for interfering substances.