Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (707 page)

   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

   Use

   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

   Interpretation

   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.

ANTICOAGULATION DNA PANEL
^†

   Definition

   The anticoagulation DNA panel tests for genetic variants in the
CYP2C9
and
VKORC1
genes that account for >50% of variation in warfarin response. Genotyping may reduce the need for INR surveillance as genotype-based dosing regimens are established.

   Variants tested by the anticoagulation panel include