[Undetectable anti-platelet factor 4/heparin antibodies with IgG-specific chemiluminescent immunoassays in a heparin-induced thrombocytopenia patient].

A 51-year-old man with a 9-month history of narrowing of visual fields and papilledema was admitted to the Department of Neurosurgery. Upon admission, glycerol was intravenously administered and heparin flushes were initiated to maintain intravenous access. Brain MRI revealed right transverse and sigmoid sinus thrombosis on hospital day 2, and the patient was treated with unfractionated heparin. On hospital day 9, the patient had a seizure and impaired mental status. Moreover, on hospital day 10, the platelet count decreased to less than half compared with that documented upon admission. The patient was then switched from heparin to argatroban because thrombosis exacerbation due to heparin-induced thrombocytopenia (HIT) was suspected. Despite negative IgG-specific chemiluminescent immunoassay for anti-platelet factor 4 (PF4) /heparin antibodies, positive functional assay led to the diagnosis of HIT. Warfarin was initiated and the platelet count was restored. Because maintaining the patient's PT-INR within the therapeutic range was difficult probably due to concomitant antimicrobial administration for complicating pneumonia, anticoagulation was switched to rivaroxaban. No bleeding or thrombotic complications developed. Thus, the presentation and clinical course should be considered for an accurate diagnosis of HIT. This is particularly important when the immunological assay is negative for anti-PF4/heparin antibodies. Furthermore, anticoagulation with rivaroxaban can be useful in the management of the subacute phase of HIT.