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effectively. Eventually the test results for a transient inhibitor are present to help understand if an NBA test result may have
become negative without special inhibitor treatment. As noted been a false positive.
earlier, a false positive result is a positive inhibitor test result,
but the person does not actually have an inhibitor. Why should I know about these tests?
Treatment products continue to change. As the structure and
Heparin, lupus anticoagulants, and non-specific inhibitors can function of treatment products change, laboratory tests de-
cause false positive test results. Heparin is a blood thinning signed to identify inhibitors of traditional products may not
medicine sometimes flushed through venous access devices, be as effective. For example, Emicizumab, also called ACE910,
like ports. Lupus anticoagulants (LAs) are certain antibodies is a treatment product currently being tested, in clinical trials,
that prevent blood from clotting in test tubes but not in people. in people with hemophilia. Inhibitors in people treated with
Finally, non-specific inhibitors are antibodies that can attach ACE910 cannot be detected using traditional clot-based inhibi-
to infused clotting factor. However, LAs and non-specific in- tor tests, like the NBA or modified NBA. To detect an inhibitor
hibitors do not prevent the infused treatment product from in someone treated with ACE910, the chromogenic assay must
working effectively. be used.
It is important to remember that an inhibitor diagnosis is made Where can I get inhibitor testing?
by a hematologist. Additional testing can help to determine Most local hemophilia treatment centers (HTCs) can provide
whether a NBA test result is a true positive or a false positive inhibitor testing with the NBA method. People with hemophil-
result. Inhibitor test results and other laboratory tests only pro- ia A, hemophilia B, and vWD type 3 who have been infused at
vide information to help the doctor make the diagnosis of an least once with clotting factor are also eligible to receive free in-
inhibitor. hibitor testing through the CDC laboratory, if they participate
in the CDC-funded program, Community Counts. Community
What are other inhibitor test methods? Counts participants receive inhibitor testing with the modified
CDC uses three other tests to confirm low-positive NBA re- NBA method. Those participants with low-positive test results
sults: the chromogenic assay, a fluorescence immunoassay also get free chromogenic, FLI, and DRVVT testing. If you are
(FLI), and the Dilute Russell Viper Venom Time (DRVVT) as- interested in participating in Community Counts, please talk
say. The chromogenic assay is more specific than the NBA, with your HTC. Most people with bleeding disorders are eli-
meaning it will better identify people who do not have inhibi- gible to participate in Community Counts.
tors. The FLI measures the amount of antibody that binds to
clotting factor 8 or factor 9. It is more sensitive than the NBA Community Counts and inhibitors
and will better identify people who truly have inhibitors. LAs, Community Counts is a public health monitoring program
non-specific inhibitors, and heparin do not cause false positive for people with bleeding disorders, funded by CDC through
test results in the chromogenic assay or the FLI. The DRVVT a cooperative agreement with the American Thrombosis and
assay does not test for inhibitors, but it identifies whether LAs Hemostasis Network (ATHN) and the US HTC Network. The
Approximately 1 in 5 people with hemophilia A, and 3 in 100 people with hemophilia B,
will develop an inhibitor.
14 Dateline Federation | Fall 2017
