Here is an interesting question from Prof Terezinha Paz Munhoz:
Mr Fritsma, Could you please help us? When the DRVVT screen is not prolonged, but the ratio of screen to confirmatory exceeds the established cutoff, what do we do? I’ve read a review by Teruya J, West AG, Suell MN. Lupus anticoagulant assays; questions still to be answered, Arch Pathol Lab Med 2007; 131: 885–9. The authors queried several experts about this subject and the conclusion is “the answers were equivocal.” I agree that our results do “not satisfy step 1 of the ISTH recommendation”, but how can we interpret this results? What do you do?
Prof. Dra Terezinha Paz Munhoz
Coordenadora do Setor de Hematologia
Laboratório de Patologia Clínica—Hospital São Lucas-PUCRS
Faculdade de Farmácia -PUCRS
Porto Alegre- RS, Brasil
Dear Prof Munhoz, thank you for contacting Fritsma Factor. I forwarded your question to Marisa B. Marques, MD, my colleague and the medical director of the special coagulation laboratory at the University of Alabama at Birmingham Hospital. Here is Dr. Marques’s answer:
George: If the initial DRVVT is not prolonged, it does not matter what the ratio is because the neutralization test is not indicated. The ratio may be positive because of the excess of phospholipid. Dr. Douglas Triplett used to say, “if you put more phospholipid in the test, it is like putting fuel on the fire—the clot will form faster”. Thus, it is not surprising that the DRVVT ratio could be positive in some cases because the DRVVT confirm has an excess of phospholipid.
By the way, did you know that Prof Munhoz is from the same city that I am, though we are not acquainted?
Thanks for the chance to respond. Marisa.
Marisa B. Marques, MD
Division of Laboratory Medicine
University of Alabama at Birmingham
Prof Munholz, one reason I sent this message to Dr. Marques, in addition to her expertise, is that she shares your nationality. I had no idea you and she are from the same city. That is quite a coincidence, many of us in the USA don’t realize the land mass of Brazil is greater than that of the US.
I’ll just add to Dr. Marques’ comments to recommend that you collect a new specimen from the patient and repeat your lupus anticoagulant profile, ensuring that you centrifuge the specimen to produce platelet poor plasma (platelet count less than 10,000/uL) and that you test using a lupus anticoagulant-sensitive partial thromboplastin time in addition to the DRVVT. For assistance, I am linking this note to a paragraph from page 71 and 72 of our recently published handbook, Marques MB, Fritsma GA, Quick Guide to Coagulation, 2nd edition, 2009, AACC Press, Washington, DC.