From Lorna Bogertman, Valley Health: Hello George, I have a question concerning lupus anticoagulant (LA) testing. We have had several requests from physicians to perform hexagonal phase LA testing only. Is it valid to perform this test without the rest of the LA profile? We have found that if we performed Stago’s LA-sensitive partial thromboplastin time (PTT-LA) and the dilute Russell viper venom time (DRVVT), the LA would have been reported as negative, however in this case the hex phase test was positive. How should this be reported? If the profile is really negative, what are the other causes of a positive hex phase test other than LA?
Category: Lupus Anticoagulant
From Ben Troyer at Med Central Health System: Should lupus anticoagulant testing be offered on a STAT basis? Our LA test volume is pretty low—we average 3–5 requests per week. We make the test available as a STAT, but I’m not sure that this is necessary or appropriate. I’d appreciate any input. Thanks!
From Kathy Doig, PhD, Michigan State University (Go Spartans!). George – what is the current thinking on how antiphospholipid antibodies (lupus anticoagulants, LAs) interfere with our assays? Does the antibody physically block the proteins so they can’t react properly even though they embed in the phospholipids (PLs)? Does it prevent them from embedding in the PLs as they should? Or is it something else entirely?
Dr. Doig gets these penetrating questions from her graduate students, sending us back to the books for answers. Here is George’s effort at a reply:
From Kelly Townsend, Tri-core Reference Laboratories, Albuquerque. Looking for opinions on what constitutes a “Laboratory Developed Test” in Coag. Obviously if the reagent kit is not FDA-cleared, it will be an LDT, but what about factor assays, etc where there is no real kit. What if you are using a kit with a different calibrator or control than the manufacturer sells/endorses? Having trouble coming up with a concise definition for LDT. Thanks, Kelly.
From Dave McGlasson, George, Has anyone got information on storing DRVV screen and confirm reagent aliquots? Can you freeze/thaw them without any loss in activity? That question has come up to me recently.
From Rose Markarian, Supervisor Hematology, Saint John’s Health Center, Santa Monica, CA: Hi George, We perform Stago’s confirmatory hexagonal phase Sta-Clot LA test for lupus inhibitor testing. We validated Stago’s recommended cut off value of ≤ 8.0 seconds several years ago when the test was implemented. Do we have to validate the cut off value with each new lot of reagent? Please advise.
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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.
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.