Summary
One of the standard distinctions between type 1 (non-immune) and type 2 (immune-mediated)
heparin-induced thrombocytopenia (HIT) is the transience of thrombocytopenia: type
1 HIT is viewed as early-onset and transient thrombocytopenia, with platelet count
recovery despite continuing heparin administration. In contrast, type 2 HIT is viewed
as later-onset (i. e., 5 days or later) thrombocytopenia in which it is generally
believed that platelet count recovery will not occur unless heparin is discontinued.
However, older reports of type 2 HIT sometimes did include the unexpected observation
that platelet counts could recover despite continued heparin administration, although
without information provided regarding changes in HIT antibody levels in association
with platelet count recovery. In recent years, some reports of type 2 HIT have confirmed
the observation that platelet count recovery can occur despite continuing heparin
administration, with serological evidence of waning levels of HIT antibodies (“seroreversion”).
We now report two additional patient cases of type 2 HIT with platelet count recovery
despite ongoing therapeutic-dose (1 case) or prophylactic-dose (1 case) heparin administration,
in which we demonstrate concomitant waning of HIT antibody levels. We further review
the literature describing this phenomenon of HIT antibody seroreversion and platelet
count recovery despite continuing heparin administration. Our observations add to
the concept that HIT represents a remarkably transient immune response, including
sometimes even when heparin is continued.
Keywords
Deep vein thrombosis - heparins - pulmonary embolism - thrombosis
