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The ICU patient

In the intensive care setting HIT is uncommon but thrombocytopenia is very common. In patients with a low or moderate risk of HIT the risk of failing to prevent a HIT associated thrombosis must be balanced against the risk of switching to an alternative anticoagulant.

Greinacher et al. (1) have outlined their approach to managing different clinical scenarios in the intensive care unit (ICU):

1. HIT is very unlikely: In a patient without thrombocytopenia or other clinical features of HIT, a positive HIT antigen test (ELISA) is reported.

ACTION: Maintain heparin and monitor platelet counts. Avoid testing for antibodies in low pretest probability situations in the future.

2. HIT is very unlikely: In a patient who presents with thrombocytopenia and/or new thrombosis, a negative ELISA is reported.

ACTION: Check for other possible reasons for platelet count decrease (e.g. order blood cultures, investigate for disseminated intravascular coagulation). Ensure sufficient levels of anticoagulation if thrombosis occurred while on heparin (e.g. anti-Xa levels). Do not repeat HIT antibody testing unless thrombocytopenia worsens or recurs or new thrombosis occurs.

3. HIT is not ruled out: Patient presents with a decrease in platelet counts, which may be explained by comorbidity, but has a weak positive ELISA (optical density <1.0 units), and a negative functional assay (or functional assay is not available).

ACTION: Switch to an alternative anticoagulant, preferably in prophylactic doses; if DTIs are used, start with a low dose (25-50% of the expected maintenance dose) and adjust dose according to the activated aPTT. Further treatment decisions should then be based on the clinical course after change of anticoagulation; for example, prompt increase of platelet counts argues for HIT. Confirm HIT with a functional test, if available (usually requires referral of the blood specimen to a reference laboratory)

4. HIT is probable: Patient presents with a decrease of platelet counts with no other definite explanation and a strong positive ELISA (>1.0 optical density units).

ACTION: Stop heparin and start alternative anticoagulation preferentially in therapeutic dose; in case of high bleeding risk, reduce dose accordingly. Confirm HIT with a functional test, if available (usually requires referral of the blood specimen to a reference laboratory).

5. HIT is very likely: Patient presents with new thrombosis and thrombocytopenia with temporal features consistent with HIT, without other obvious explanation, and with a positive ELISA.

ACTION: Stop heparin and start alternative anticoagulant in therapeutic dose. Confirm HIT by a functional test, if possible.

1.Selleng K, Warkentin TE, Greinacher A. Heparin-induced thrombocytopenia in intensive care patients. Crit Care Med 2007; 35(4):1165-76

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