I was given Arixtra for the exact reason Al pointed out - I tested positive for HIT. The hematologists were pretty sure it was a false positive (I'll be re-tested in October, just to be sure) but, decided to not take a chance for which I'm actually quite grateful . As far as we know, our insurance covered the Arixtra so am thankful for that too. Thank you Ross for asking this question though, just to be sure! And thanks to Al for his quick response.