HIT vs. HAT

Here’s a good question about two entities that sound the same (but aren’t).

Q. What is the difference between heparin associated thrombocytopenia (HAT) and heparin induced thrombocytopenia (HIT)?

A. Heparin-induced thrombocytopenia (HIT) is defined as a decrease in platelet count during or shortly after heparin exposure. There are two types of HIT:

1. HIT type I (used to be called heparin-associated thrombocytopenia) – a benign, probably non-immune form of HIT that is not associated with an increased risk of thrombosis. It is mild, with platelet counts rarely dipping below 100,000. It affects up to 10% of patients receiving heparin treatment, and it disappears with withdrawal of heparin.

2. HIT type II – an immune-mediated type of HIT that is associated with an increased risk of thrombosis. It is associated with significant morbidity and mortality if unrecognized.

Here is a good article that goes into greater depth on HIT, especially the second type:
http://www.thrombosisjournal.com/content/3/1/14

Photo credit: Amanda Dowling (http://www.flickr.com/photos/tinkerroll21/3279134315/)