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Antiphospholipid Antibodies in Patients With Lupus Anticoagulant Prozone Effect


Murphy CH1, Jin J2, Zehnder JL1. Am J Clin Pathol. 2019 Oct 10. pii: aqz151. doi: 10.1093/ajcp/aqz151. [Epub ahead of print]

Author Information

1 Department of Pathology, School of Medicine, Stanford University, Stanford, CA.

2 Stanford Coagulation and Hemostasis Laboratory, Stanford Medical Center, Palo Alto, CA.



Lupus anticoagulant (LAC) is typically associated with thrombosis but also rarely with hemorrhage. Some patients exhibit a prozone effect on LAC testing. Antiphosphatidylserine/prothrombin (aPS/PT) antibodies may provide a mechanism for both hemorrhage and prozone effect. Our goal was to evaluate whether antibody specificities, isotypes, and titers were associated with LAC prozone effect, factor II levels, hemorrhage, and thrombosis.


Patients with prozone effect noted on LAC testing were entered into a database over 3 years. Factor II activity and aPS/PT antibody testing were performed when a sufficient residual sample was available.


All patients with LAC prozone effect and antibody testing were positive for at least 1 class of aPS/PT antibodies. In addition, aPS/PT IgG titers were significantly associated with thrombosis and significantly inversely associated with factor II levels.


In prozone effect patients, aPS/PT antibodies are associated with LAC prozone effect as well as thrombosis and decreased factor II levels.