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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From Don Wahl, Sanford Health: What are the recommended tests to include in a lupus anticoagulant/antiphospholipid antibody (LA/APL) panel? Is there an antiphospholipid group that gives recommendations? Thank you, Don.
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From Courtney Jackson at Oschner in Louisiana: We use a commercial pooled normal platelet-free plasma (PNP) for our prothrombin time (PT) and partial thromboplastin time (PTT) mixing studies. When we mix it with saline for our controls, we don’t get a normal PTT until the ratio is 4 plasma to 1 saline. We get close to normal at a 1:1 mix, but not in normal range. Often we get no clot at all (>150 seconds) at a 4 saline to 1 pool mix. The pool control is within normal limits. A similar finding is occuring with our PT mixing study as well. I find this counterintuitive–the mix of saline and normal pool should be close to normal even at 20% saline, and normal at 50%. Any thoughts? Thank you for your input.
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From “Danagah” (originally posted February 23, 2012):
Hi, George, have you seen the situation when, in the 1:1 immediate mix of a partial thromboplastin time (PTT) mixing study, the PTT is longer than the patient’s initial PTT? The patient does not appear to be on heparin (data to follow):
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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 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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From “Balasubm” at Einstein Healthcare in Philadelphia: Hi George, I have a 74 year old female renal dialysis patient who is asymptomatic with prolonged prothrombin time (PT) of 38 seconds and activated partial thromboplastin time (APTT, PTT) of 116 seconds, with a normal thrombin time. Mixing performed immediately reveals PT of 30.3 seconds (N 9.5-13.5) and APTT of 84.3 seconds (N 22-38). After incubation the PT went to 31.6 seconds and APTT to 86.6 seconds. The specimen was drawn from the dialysis catheter, however, these lines do not use heparin. Could you please tell us what you think these results mean?
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From “Japgi,” I have a 6 year old boy, well till a month back, when he had a post-traumatic gum bleed. The bleed was stopped after about half an hour, but a small ooze restarted and stayed for 3 days. His prothrombin time (PT) is 14 seconds (RI 11–16), activated partial thromboplastin time (APTT, PTT) is 46.4 seconds (RI 30–40). The prolonged PTT corrected with normal plasma 1:1 is 38.1 seconds. There was no correction with 1:1 mix of factor VIII-deficient plasma, 43.1 seconds; factor IX-deficient plasma, 43.1; or factor XI-deficient plasma, 41.1. The entire exercise was performed on two separate samples a week apart. There is no history of bleeding in the family, transfusions. After the first test the patient has been running a cold with fever. What is this and what can we do to confirm? Thank fully there are no further bleeds.
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Lupus Anticoagulant, Mixing Studies | George Fritsma | 
February 28, 2013 6:47 pm | 
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