The 4Ts Score for HITS - MedSchool
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The 4Ts score is a means of stratifying risk of heparin-induced thrombocytopaenia syndrome (HITS), based on the onset and severity of thrombocytopaenia following heparin administration, as well as presence of features of HITS.
Timing of Platelet Count Fall
Thrombosis / Other Sequelae
Other Causes of Thrombocytopaenia
  • Low probability (1-3) - HITS unlikely; negative predictive value 99.8%
  • Moderate probability (4-5) - risk of HITS ~13%
  • High probability (6-8) - positive predictive value 64%


 Crowther MA, Cook DJ, Albert M, Williamson D, Meade M, Granton J, Skrobik Y, Langevin S, Mehta S, Hebert P, Guyatt GH. The 4Ts scoring system for heparin-induced thrombocytopenia in medical-surgical intensive care unit patients. Journal of critical care. 2010 Jun 1;25(2):287-93.
Cuker A, Gimotty PA, Crowther MA, Warkentin TE. Predictive value of the 4Ts scoring system for heparin-induced thrombocytopenia: a systematic review and meta-analysis. Blood. 2012 Jan 1:blood-2012.
Lo GK, Juhl D, Warkentin TE, Sigouin CS, Eichler P, Greinacher A. Evaluation of pretest clinical score (4 T's) for the diagnosis of heparin?induced thrombocytopenia in two clinical settings. Journal of Thrombosis and Haemostasis. 2006 Apr;4(4):759-65.