4Ts Score for Heparin Induced Thrombocytopenia Calculator

Thrombocytopenia Select Platelet fall greater than fifty percent and nadir at least twenty thousand Platelet fall thirty to fifty percent or nadir ten to nineteen thousand Platelet fall less than thirty percent or nadir below ten thousand Timing of Platelet Count Fall Select Clear onset between day five and ten or within one day with prior heparin exposure Consistent with day five to ten but not clear or onset after day ten Platelet fall too early without recent exposure Thrombosis or Other Sequelae Select New thrombosis skin necrosis or acute systemic reaction Progressive or recurrent thrombosis or suspected thrombosis None Other Causes of Thrombocytopenia Select No other cause evident Possible other cause Definite other cause present 4Ts Score for Heparin Induced Thrombocytopenia: Explanation and Clinical Context The 4Ts Score is a clinical prediction tool used to estimate the probability of heparin induced thrombocytopenia in patients receiving unfractionated or low molecular weight heparin. It evaluates four domains including the degree of thrombocytopenia timing of platelet count fall presence of thrombosis and the likelihood of alternative causes of thrombocytopenia. The total score ranges from zero to eight and stratifies patients into low intermediate or high probability categories for HIT.

A low score suggests HIT is unlikely and heparin therapy may often be continued while intermediate and high scores warrant immediate discontinuation of heparin and further laboratory testing with immunologic and functional assays. Early risk stratification using the 4Ts Score reduces unnecessary testing prevents inappropriate anticoagulant changes and improves patient safety.