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HIT Calculator Algorithm Rationale and Derivation

Adverse events with use of heparin are not common, but can be life and limb threatening. Diagnosis of such events can be nuanced, and may lead to excessive interventions in both monitoring and treatment. Guidelines and algorithms now exist to aid in diagnosis and reduce unnecessary interventions. The calculator incorporates the 4T's score and the guideline recommendations from reference 6 in a form which can be applied to any heparin patient at any time during the course of current or previous treatment. Decision support is incorporated for heparin discontinuation. It is recommended that the advice of a consultant be obtained regarding choice and management of alternative anticoagulants.

Heparin-induced thrombocytopenia (HIT) has a poor prognosis unless the use of heparin is discontinued and an alternative anticoagulant such as a direct thrombin inhibitor or factor Xa inhibitor is substituted. Sentinel characteristics may include:

Problems are associated with both diagnosis and treatment of this condition. These include:

Strategies to optimize outcomes:

For a general overview of Heparin Induced Thrombocytopenia, click here

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  2. Hudoba M, Dalal B, Warkentin T, et al. Toward better utilization of laboratory resources: The impact of a mandatory 4T's pretest clinical assessment form on the diagnosis of heparin-induced thrombocytopenia. BC Medical Journal 2012; 54(5): 244-247.
  3. Coutre S. Heparin induced thrombocytopenia. UpToDate online ver. 15.2
  4. Lo GK, Juhl D, Warkentin TE, et al. Evaluation of pretest clinical score (4 T's) for the diagnosis of heparin-induced thrombocytopenia in two clinical settings. J Thromb Haemost 2006; 4:759.
  5. Warkentin TE, Linkins L-A. Non-necrotizing heparin-induced skin lesions and the 4T’s score. J Thromb Haemost 2010; 8:1483–5.
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  7. Takemoto C, Streiff M. Heparin-induced thrombocytopenia screening and management in pediatric patients. Hematology Am Soc Hematol Educ Program. 2011;2011:162-9.
  8. UIC College of Pharmacy Drug Information Group. What are the new recommendations for frequency of platelet monitoring in patients with heparin-induced thrombocytopenia? Available from: Accessed 2013 Oct 1.