The more we come to understand the pathophysiology of heparin-induced thrombocytopenia (HIT) syndrome, the more we realize that HIT is a rather unusual immune response. One peculiar feature of HIT is the transient character of the antibodies. After cessation of exposure to heparins, the antibodies tend to disappear after 40-100 days. If re-immunization occurs, it generally takes at least 4 days to redevelop antibodies (if they are formed at all). We report about a patient who most likely developed platelet-activating IgG-specific platelet factor 4 (PF4)/heparin antibodies after knee surgery, experienced a transient ischemic attack years later [when HIT was diagnosed by using PF4/heparin ELISA] and presented a high number of these antibodies even 4 years after this first diagnosis of HIT without further re-exposure to heparin.
Keywords: HIT; heparin; platelets.