Blood, 15 April 2003, Vol. 101, No. 8, pp. 2903-2903
Heparin-induced thrombocytopenia in medical patients
Girolami and colleagues (page 2955) report their study of the
incidence and clinical impact of heparin-induced thrombocytopenia (HIT)
in 598 medical patients who received subcutaneous unfractionated heparin for various prophylactic and therapeutic indications. They
found that 5 of 598 patients (0.8%) developed HIT (or about 1% at 2 weeks by time-to-event analysis). Remarkably, 3 of the 5 patients
(60%) developed one or more HIT-associated thrombotic events (2 fatal
outcomes). The odds ratio for thrombosis observed was very high at 40.8 (95% CI, 5.2-162.8; P < .001) and parallels the known
high risk of thrombosis previously observed in surgical patients who
develop HIT (Warkentin et al, N Engl J Med.
1995;332:1330-1335). Thus the main conclusion is stark: although HIT
occurs somewhat less often in medical than in surgical patients (1% vs
3%-5%), it remains a very serious, life-threatening adverse drug
effect. Thus their findings support the College of American
Pathologists's recent recommendation (Warkentin, Arch Pathol Lab Med.
2002;126:1415-1423) that routine monitoring of platelet counts be
performed in medical patients receiving unfractionated heparin in
prophylactic or therapeutic doses.
The study provides other interesting insights. For example, the authors
found that previous exposure to heparin (occurring more than 3 months
earlier) was not associated with an increased risk of
developing HIT. This is consistent with the emerging view that typical
immunologic memory is not a feature of HIT (Warkentin and Kelton,
N Engl J Med. 2001;344:1286-1292). Also, Girolami and
coworkers presented the serial platelet counts in their 5 HIT patients:
this illustrates that medical patients who develop HIT do not display
the "inverted V" platelet count profile characteristic of HIT after
surgery (which happens because the rising platelet count following
surgery is then complicated by the falling platelet count of HIT;
see Warkentin et al, cited above). The authors should be congratulated
for illuminating how, and how often, HIT impacts medical patients
receiving unfractionated heparin.
Theodore E. Warkentin
McMaster
University
