|Values are valid only on day of printing.|
Factor XI inhibitors typically arise in patients with congenital XI deficiency (hemophilia C), after infusion of fresh frozen plasma or factor XI concentrates. Acquired factor XI inhibitors rarely occur spontaneously.
Detection and quantitation of inhibitor to coagulation factor XI
Normally, there is no inhibitor, ie, negative.
If the screening assays indicate the presence of an inhibitor, it will be quantitated and reported in Bethesda (or equivalent) units.
If the presence or type of inhibitor is unknown, LUPPR / Lupus Anticoagulant Profile should be ordered, except for screening studies in patients with known hemophilia A or B.
Occasionally, a potent lupus-like anticoagulant may cause false-positive testing for a specific factor inhibitor (eg, factor VIII or IX); see preceding Caution statement.
Not useful for the detection of a lupus-like circulating anticoagulant inhibitor or other inhibitors not specific for coagulation factors.
Not useful for the detection of a nonspecific circulating anticoagulant.
FACTOR XI ACTIVITY ASSAY
Normal, full-term newborn infants or healthy premature infants may have decreased levels (> or =10%) which may not reach adult levels for > or =180 days postnatal.*
*See Pediatric Hemostasis References in Coagulation Studies in Special Instructions.
FACTOR XI INHIBITOR SCREEN
1. Feinstein DI: Acquired inhibitors of blood coagulation. In Hematology: Basic Principles and Practice. Edited by R Hoffman, EJ Benz Jr, SJ Shattil, et al. New York, Livingstone Press, 1991, pp 1380-1394
2. Kasper CK: Treatment of factor VIII inhibitors. Prog Hemost Thromb 1989;9:57-86