I received a question through the American Society for Clinical Laboratory Science (ASCLS) Consumer Forum, from whence come many thorny hemostasis questions. This question was forwarded by Prof. Bernadette Rodak of Indiana University. I’ll quote (with edits for brevity), but have masked the consumer’s identity:
“I had a cerebral thrombosis in March 2009 at the age of 22. I have been tested 7 times for lupus anticoagulant (LAC) while on warfarin over the past 18 months and 4 of 7 have come back positive. This has resulted in my hematologist prescribing warfarin for the ‘foreseeable future.’”
From attached lab results, the questioner was consistently negative for LAC using hexagonal phase phospholipid neutralization of the partial thromboplastin time (PTT), and marginally positive (ratios of 1.3 or 1.4) for LAC, using the dilute Russell viper venom time (DRVVT) assay with neutralization, 4 out of 7 times over 12 months. She was once tested for anti-cardiolipin antibody, the results were negative.
“My hematologist is uneasy with taking me off anticoagulants because of the location of my previous clot. How do I ease her mind? Can you reference any articles or journals that support your statements about the effect of warfarin on LAC testing?”
“How will Lovenox injections affect the test results? I know the objective is to get me completely off the anticoagulants for a “clean” test, but if my doctor suggests this, is it an option?”
Beginning with the usual disclaimers about avoiding diagnosis and treatment discussions online, I suggested the DRVVT results seem to indicate LAC, but the best possibility for diagnosing or ruling out antiphospholipid syndrome was to test for anti-cardiolipin antibody and beta-2-glycoprotein 1 antibody (IgG and IgM). While switching to Lovenox is a medical decision best made by the physician, LAC testing by DRVVT while on Lovenox is reliable.
Some questions to our participants:
I promised the consumer some follow-up to my original response. About the DRVVT results, while it is clear warfarin prolongs the assay, it seems the ratio of the neutralized to non-neutralized clotting times could still be presumptive, especially when the test was repeatedly positive. Do you agree? Does she have LAC?
Also, do you agree the patient could be tested while on Lovenox? Thanks for your help.