A small but substantial proportion of patients with hemophilia A develop immediate acting factor VIII inhibitors, the diversity and complexity of which create a diagnostic challenge in the laboratory, according to authors of a recent observational study.
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The great majority of the inhibitor-positive patients in the 4,900-patient study had classical FVIII inhibitors, which are typically time- and temperature-dependent and react more slowly in mixing studies, the researchers reported.
By contrast, about 1 in 10 patients demonstrated immediate acting inhibitors, and of those, some had lupus anticoagulants, some had factor VIII inhibitors, and some had both, according to Shrimati Shetty, PhD, of the National Institute of Immunohaematology in Mumbai, India, and her colleagues.
“There is a possibility of misdiagnosis of the patient when they present for the first time,” the researchers wrote. The report is in Thrombosis Research.
In the case of immediate-acting inhibitors, use of ELISA or chromogenic assays alongside lupus anticoagulant testing may help clarify the diagnosis; however, those tests are costly and may not be routinely available.
In the study by Dr. Shetty and her colleagues, patients in India with congenital hemophilia were initially screened for inhibitors. A total of 451 were found to be positive, and of those, 398 were observed to have classical factor VIII inhibitors, while the remaining 53 had immediate-acting inhibitors.
Looking specifically at hemophilia A patients with immediate-acting inhibitors, which comprised 48 of those 53 patients, the majority, or 42 patients, were positive for lupus anticoagulants, and of those, 38 were positive for both lupus anticoagulants and factor VIII inhibitors, while 4 patients were positive for lupus anticoagulants only.
“These are a heterogeneous group of antibodies interfering with all phospholipid dependent reactions,” the researchers wrote.
Properly interpreting factor inhibitor assays is an important step that helps guide later management of inhibitor-positive patients, according to Dr. Shetty and her coauthors.
“Once the patients become positive for inhibitors, they have to opt for alternate modalities of treatment, i.e. bypassing agents like activated prothrombin complex concentrate and activated recombinant factor VII, which are much more expensive,” they wrote.
In light of the diagnostic difficulties they highlighted, Dr. Shetty and her coauthors recommended a “systematic approach” to testing. Both factor VIII and factor IX assays need to be conducted, along with a lupus anticoagulant test. For inhibitor titer, either chromogenic assays or ELISA tests are recommended, they wrote.
Dr. Shetty and her coauthors reported that they had no conflicts of interest.
SOURCE: Patil R et al. Thromb Res. 2018 Dec;172:29-35.