|Values are valid only on day of printing.|
Detection and titering of coagulation inhibitor to the specific factor requested, primarily factor IX in patients with hemophilia B
Testing begins with coagulation factor IX activity assay with dilutions to evaluate assay inhibition; if the factor IX activity assay is decreased, an inhibitor will be performed to look for specific factor IX inhibition. If specific inhibition is apparent, it will be titered.
Factor IX inhibitors arise in patients with severe hemophilia B after factor IX transfusion. Patients with factor IX inhibitors may also develop anaphylactic reactions in response to factor IX infusions. Acquired factor IX inhibitors, occurring in previously healthy people, are exceedingly rare.
FACTOR IX ACTIVITY ASSAY
Normal, full-term newborn infants or healthy premature infants may have decreased levels (> or =20%), which may not reach adult levels for > or =180 days postnatal.*
*See Pediatric Hemostasis References in Coagulation Studies in Special Instructions.
FACTOR IX INHIBITOR SCREEN
Normally, there is no inhibitor (ie, negative result).
If the screening assays indicate the presence of an inhibitor, it will be quantitated and reported in Bethesda (or equivalent) units.
This test is not useful for detecting presence of inhibitors directed against other clotting factors and is not useful for the detection of a nonspecific circulating anticoagulant.
This assay will not detect presence of lupus anticoagulants.
If presence or type of inhibitor is unknown, PROCT / Prolonged Clotting Time or LUPPR / Lupus Anticoagulant Profile should be ordered.
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.
1. Feinstein DI, Rapaport, SI: 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. Chitlur M, Warrier I, Rajpurkar M, et al: Inhibitors in factor IX deficiency a report of the ISTH-SSC international FIX inhibitor registry (1997-2006). Haemophilia 2009;15(5):1027-1031