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Simultaneous Occurrence of Lupus Anticoagulant and Factor VIII Inhibitors in Hemophilia
To the Editor: The letter published in the November 1997 issue, regarding simultaneous occurrence of lupus anticoagulant (LA) and factor VIII inhibitors [1,2], is very interesting. We agree with Dr. D.A. Triplett that it is of critical importance to differentiate an LA from a factor VIII inhibitor. Strict observance of the criteria recommended by the SSC Subcommittee on Lupus Anticoagulant/Phospholipid-Dependent Antibodies [3] is essential for this purpose. More than one test, with different assay principles, is necessary to screen for an LA, mainly in patients with other simultaneous coagulation defects, such as a neutralizing inhibitor or a factor deficiency. In a recently published study of 170 consecutive hemophilia A patients, we found 36 hemophiliacs who fulfilled the criteria for the diagnosis of LA, 18 of them with a time-dependent effect. It is possible that subjects with a strong time-dependent effect may have both a factor VIII inhibitor and an LA (n โซืกโฌ 12) [4]. LAs were diagnosed based mainly on diluted Russell viper venom time (dRVVT). The activated partial thromboplastin time (APTT) is affected by factor VIII inhibitors; however, the platelet neutralization procedure of the APTT showed similar results to those obtained for dRVVT, except in three patients with positive dRVVT, for whom the shortening of the PNP was not sufficient to be considered positive. In our study, the StaclotLA results agreed with those from dRVVT; 8/8 were positive on LAs and 3/3 were negative on factor VIII inhibitors. We believe that factor VIII inhibitors could be masked by LA and the misdiagnosis could delay the prescription of the appropriate therapy [5]. The above evidence stresses the need to develop a specific test to identify factor VIII inhibitors without interference of LA, and vice versa.