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Subject: Anticoagulants, Circulating
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Circulating anticoagulants are antibodies that inhibit the function of specific coagulation factors, most commonly factor VIII or IX. They may be acquired following multiple transfusions in hemophiliacs (alloantibodies) or spontaneous (autoantibodies)—most commonly against factor VIII. Lupus anticoagulants (LA) are sometimes clinically associated with circulating anticoagulants
A circulating anticoagulant is suspected under two conditions:
A patient with hemophilia A or B who has had multiple transfusions and whose bleeding does not stop on infusion of the missing factor
A middle-aged person, especially if diagnosed with lymphoma, or a postpartum patient who develops unprovoked hemorrhages
In a patient with hemophilia A or less commonly B, serial determinations of factor A or B show no elevations following infusions.
In a patient with no previous bleeding history, the finding of a prolonged PTT should raise the suspicion of an acquired circulating anticoagulant. If incubation at 37°C of half normal plasma with half patient's plasma for 1–2 hours does not correct the prolonged PTT, a circulating anticoagulant is diagnosed (unless the patient is receiving unfractionated heparin, or the sample is contaminated with heparin).
Specific titration of the inhibitor's potency is performed for either factor VIII or IX inhibitors, and the results are reported in Bethesda Inhibitory Units.