Published in:
01-08-2010 | Correspondence
Diagnosing heparin induced thrombocytopenia in critically ill patients
Published in: Intensive Care Medicine | Issue 8/2010
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Sir: Heparin-induced thrombocytopenia (HIT) is one of the most serious drug reactions occurring in intensive care patients and is difficult to manage because the predictive value of the laboratory investigations is imperfect and the treatment involves anticoagulating thrombocytopenic patients at a high risk of bleeding. Since investigations for HIT have poor specificity, current American and British guidelines recommend that the probability of HIT is initially judged clinically [1, 2] and a scoring system, known as the 4 Ts score (Table 1) is recommended [3].
Table 1
The 4 Ts pretest scoring system for heparin-induced thrombocytopenia (HIT) [3]
|
0 Point
|
1 Point
|
2 Points
|
|
|---|---|---|---|
|
Degree of thrombocytopenia
|
Platelet count decrease 30% or platelet nadir <10 × 109/L
|
Platelet count decrease 30–50% (or >50% decrease resulting from surgery) or platelet nadir 10–19 × 109/L
|
Platelet count decrease >50% and platelet nadir >20 × 109/L
|
|
7%a
|
7%a
|
85%a
|
|
|
Timing of platelet count decrease
|
Platelet count decrease <4 days without recent exposure
|
Consistent with immunization but unclear history; onset after day 10; decrease >1 day (heparin exposure 1–3 months ago)
|
Clear onset between days 5 and 10 or platelet decrease within 1 day (heparin exposure within 30 days)
|
|
52%a
|
7%a
|
40%a
|
|
|
Thrombosis or other sequelae
|
None
|
Progressive or recurrent thrombosis; nonnecrotizing (erythematous) skin lesions; suspected thrombosis not yet proven
|
New thrombosis (confirmed); skin necrosis; acute systemic reaction postintravenous UFH bolus
|
|
59%a
|
4%a
|
37%a
|
|
|
Other causes for thrombocytopenia
|
Definite
|
Possible
|
None apparent
|
|
22%a
|
63%a
|
15%a
|