From Deborah Whetzel, Children’s Hospital of the King’s Daughters, Norfolk, VA: We’ve had a couple patients lately that demonstrated inhibition but their factor VIII results are within normal limits or even elevated. The result values differ 30–40% typically between dilutions but as they’re diluted more, the values go up to 300 or 400%. FVIII values that high seem really odd to me. We dilute to 1:160, as I’ve seen recommended, with results to that point continuing to get higher. Have you seen this occur and is there something that we should be doing? Thanks for your help.
Category: Lupus Anticoagulant
From Aliaa Amer: Hi George, we are using Actin FSL for our routine activated partial thromboplastin time (APTT, PTT). Whenever we get a prolonged APTT that is >5 s above the upper limit of the norm range we do mixing studies, both immediate and 2 h incubation using 1:1 and 4:1 mix, the latter to detect weak lupus anticoagulant (LA). In many instances we get full correction and we proceed to factor assays which turn out to be normal. Then we test for LA using the dilute Russell viper venom time (DRVVT). To our surprise we find it is positive for a mild LA (LAS/LAC = 1.5, our cut off is 1.2) which could not be detected even by the 4:1 preparation. Do you have any explanation for this? We are using the Siemens BCS analyzer.
Here is a message about the dilute Russell viper venom time assay (DRVVT) for lupus anticoagulant (LA) from international expert Thomas Exner, HAEMATEX, Sydney, Australia:
It was a pleasure to meet you at the International Society on Thrombosis and Haemostasis (ISTH) meeting recently. I would like to respond an interesting question raised on July 16, 2013 in your Fritsma Factor website. Best wishes.
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.
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.
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?
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?