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Mixing Study: LA Effect?

Hello Mr. Fritsma! My name is Agustin Rodriguez and I am a haematologist from Spain. I have a question for you, if you are so kind to ansxwer it: I have a patient with a lupus anticoagulant. His PTT  (aPTT) is 46 s; normal aPTT is 30 s in my laboratory. The inmediate mixing study 1:1 with normal plasma is 52 s. Can aPTT be more prolonged after mixing with normal plasma than the basal patient aPTT? In most patients with LA, the aPTT fails to correct with normal plasma but there is no prolongationover the initial aPTT. Which is the explanation for this question?
Best regards from Spain, Agustin Rodriguez, MD Haematologist, Toledo Hospital (Virgen de la Salud), Spain.
Hello, Dr. Rodriguez, and thank you for your question. Your laboratory is experiencing a phenomenon called “lupus anticoagulant effect.” This seems to occur when using an ellagic acid-based PTT reagent, and does not occur when using PTT reagents that employ particulate activators such as silica. I have been unable to find any documentation of “lupus anticoagulant effect” in scientific literature, reports of the effect seem to be purely anecdotal. The theory, unproven, is that the normal plasma provides a cofactor, perhaps β-2-glycoprotein 1, that potentiates the lupus anticoagulant in the mixture.
I must thank my San Antonio, Texas friend and colleague, Dave McGlasson, for assisting with this entry. In the absence of published data, I needed confirmation from a technical expert. I invite our participants to contribute their experience.
Comments (4)
Lupus Anticoagulant
Chris Ferrell
Nov 20, 2014 7:27pm

Chris Ferrell wrote, Hi George, Mar
Chris Ferrell wrote, Hi George, Marlies Ledford-Kraemer published a lupus anticoagulant article a few years ago in The Clotting Times and mentioned this phenomenon. It’s called the cofactor effect and is diagnostic of a lupus anticoagulant. We see it about once every other year.

Ali Sadeghi-Khomami
Nov 20, 2014 7:13pm

This comment was emailed to George from Dr. Ali Sade
This comment was emailed to George from Dr. Ali Sadeghi-Khomami:

Hi George, I would like to emphasize that “LA-cofactor effect” is not limited to aPTT assays. For a recent dRVVT report on this effect after mixing with pooled normal plasma see, Optimisation of lupus anticoagulant tests. Thrombos Haemostas 2014, 736-42. I have seen numerous articles reporting this phenomenon but the following description is from A clinical study of the lupus anticoagulant, Blood 1976, 499-509:
“Loeliger, in 1959, was the first to demonstrate that a cofactor in normal plasma was necessary for maximal action of the lupus anticoagulant.This cofactor, which potentiates the inhibitory action of the lupus anticoagulant, is responsible for the augmentation effect. In 1965, Yin and Gaston demonstrated that the cofactor and the anticoagulant had to be present in correct proportion for the anticoagulant to exert its maximal activity. They postulated that the cofactor was a gamma globulin. A detailed study by Rivard, Schiffman, and Rapaport showed that the cofactor was: (1) unstable at 56C for 30 min; (2) minimally absorbed by BaSO4 or Al(OH)3; (3) of a molecular weight of 200,000 on gel filtration; and (4) precipitable between 50–75% (NH4)2S04 saturation. Although these characteristics are similar to those of complement, complement levels in our patients were variable and did not correlate with the anticoagulant’s activity. The augmentation effect of the cofactor was demonstrated in 67% (20 of 30) of our patients. The absence of the augmentation in the remaining ten patients may reflect the heterogeneity of the population of patients with the lupus anticoagulant and/or the crucial requirement of appropriate ratios of cofactor to anticoagulant.(4)”

Dave McGlasson
Nov 20, 2014 12:35pm

I found the original article I was looking for: Loeliger
I found the original article I was looking for: Loeliger A. Prothrombin as cofactor of circulating anticoagulant in systemic lupus erythematosus. Thromb Diath Haemorrh 1959;3:237–56. I think this was the original article on the lupus cofactor subject.

Dave McGlasson
Nov 20, 2014 9:43am


I found 5 articles that discuss the so-called lup

I found 5 articles that discuss the so-called lupus cofactor effect that causes the prolongation of the mixing studies. See the following:

Tripodi A. To mix or not to mix in lupus anticoagulant test: that is the question. Semin Thrombos Hemost 2013;4:385-9.

Horrelouh MH, et al: Biological and clinical heterogeneity of lupus and lupus-like anticoagulant in fifty-seven patients. J Med 1987,1893:199–217.

Lo SC, et al: Comparison of laboratory tests used for identification of the lupus anticoagulant. Amer J Hematol 1989, 30:213–20.

Megrath M. Lupus cofactor phenomenon. J Clin Pathol 1989,42:264.

Clyne LP. Plasma requirement for expression of lupus-like anticoagulant. Folia Haematologica int Ma Klin Morphol Blutforsch 1986;113:841–4.

Hope this helps.

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