From Bonnie Brozak-Sarandos, MT(ASCP)SH, Hematology and Coagulation Technical Specialist, ProHealth Care Laboratories, Waukesha Memorial Hospital:
Hi George, When performing the Staclot lupus anticoagulant (LA) test, the difference between Staclot 1 and Staclot 2 used to use a cutoff value of 8 seconds. We have been told by the reagent manufacturer that we should establish our own cutoff with each new lot number and use 4sd above the mean . The reagent supplier suggested using either purchased normal donor samples or using our own patient population. Using our purchased normal donors we now have a cutoff of 10.8 seconds. When we use a mixture of our normal patients and some purchased normal donors, it rises to 16.0. This is a big difference, and it is exactly what the reagent supplier said would happen, but what is right? What is the right way to establish this important cutoff? What about the patient who falls between 10.8 and 16.0? Just wondering if you know what others are doing or what experience you have with this change.
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Hello Geo, I have a question about lupus anticoagulant (LA) testing. Before I go off and tell people wrong I thought I would run this by you. Situation is, we have physicans who want to run antiphospholipid syndrome panels on patients who have a history of having a clot (one time usually). The activated partial thromboplastin time (PTT) is in normal range as are the prothrombin times (PTs). If they likely had an LA wouldn’t the PTT be prolonged? Is there something I am missing here?
Secondly they are ordering it on patients who are currently on heparin, which is a no no too. Right? Let me know, before I start telling these doctors that the test is not appropriate. Thanks, Lindsey Davenport-Landry.
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There are three helpful comments appended to our December 5, 2012 Delta Checks for PT, PTT, Fg, and D-dimer post. One came from “goblue,” whom I surmise is a University of Michigan Wolverines fan (sorry about that South Carolina game): “While administering Xarelto (rivaroxaban), will this give a false positive result on lupus anticoagulant (LA) tests?”
Yes, as rivaroxaban is a direct anti-Xa anticoagulation, it prolongs the PTT and interferes with PTT-based LA testing. On the basis of physiology and mechanism, the DRVVT-based LA assay should still work, however if any one has checked this out in the laboratory, please add your comment here. Geo.
From Mahnaz Sairi, Associate Director of Hematology, MBHN: Hi George: What is the highest limit we can report For FVIII? And how we determine this? Is it by clinical significance or by instrument linearity?
Also, should we still do lupus anticoagulant (LA) testing if both the prothrombin time (PT) and partial thromboplastin time (PTT) are normal?
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From David Summers: I have a question regarding the following lab results and all clinical symptoms which seem to represent systemic lupus erythematosus (SLE):
- PTT LA 52 seconds, reference limit 40 seconds
- DRVVT screen 44 seconds, reference limit 42 sec
- Antithrombin antigen 39 mg/dL, reference interval 18–33 mg/dL
- Protein C activity 13%, reference interval 70–180%
- There is a negative anti-nuclear antibody (ANA) test.
Would this person be considered SLE positive?
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From Scott Miller, St. Mary’s of Michigan Medical Center. Is there any consensus on whether anti-phospholipid antibodies (APAs) like lupus anticoagulant (LA) have any effect on prothrombin times and international normalized ratios (PT/INRs)? We have a patient who has been tested positive in the past for LA, and her INRs consistently run a bit higher in the lab (2.2) vs. a point-of-care (POC) device (1.7). Some studies conclude that there is no significant and consistent relationship. Others suggest there is, but that it may depend more on the type of reagent or platform. If the presence of APAs like LA is an issue, are there any guidelines on how a physician is to monitor therapy in a LA positive patient, especially considering the tendency for LA titers to rise and fall over time?
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From Sylvia Bunting, Children’s Healthcare of Atlanta: We do an immediate and incubated mixing study. For deciding on whether there is a time-dependent inhibitor, what criteria do you use to decide that the PTT was prolonged after incubation? Any prolongation beyond the immediate mix PTT? Thanks.
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Here is a question that appeared on the Clinical Laboratory Science (CLS) Educators’ list: “We are trying to figure out the principle, procedure for the tissue thromboplastin inhibition (TTI) test. We are aware that it seemingly is no longer performed, but feel there is a good chance that the ASCP could potentially ask questions about it on their certification exam. Can anyone clarify this test for us? Somehow we are having trouble understanding what we are finding in the literature.
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Lupus Anticoagulant, Mixing Studies | George Fritsma | 
February 28, 2013 6:47 pm | 
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