P Heparin Dose Dependence in HIT

Analysis of individual patients with HIT often shows dose-dependence; that is, mild thrombocytopenia during sc heparin prophylaxis is followed by a marked drop in platelet count if the patient then receives therapeutic-dose heparin (Warkentin, 2006a).

However, dose-dependence of HIT is not readily apparent when reviewing prospective studies of HIT (Tables 2 and 3). However, this could be explained by differences in frequency of HIT among different patient populations that confounds the influence of heparin dose. For example, among medical patients, porcine UFH appears to be more likely to result in HIT when given in therapeutic, rather than prophylactic, doses. This difference, if real, could reflect dose-dependence of heparin in HIT. On the other hand, the relatively high frequency of HIT in surgical patients (up to 5%) receiving "only" prophylactic-dose porcine UFH more likely reflects differences in risk related to this surgical patient population.

Dose-dependence has also been reported to be associated with a higher incidence of anti-PF4/heparin antibody formation, but not a higher frequency of

HIT, following admission to hospital for ACS and percutaneous coronary intervention (PCI) (Gluckman et al., 2005; Matsuo et al., 2005).

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