Category 2 Points 1 Point 0 Points Thrombocytopenia >50% fall or Nadir of 20-100 x 109/L 30% - 50% fall or Nadir of 10-19 x 109/L <30% fall or Nadir of < 10 x 109/L Timing of platelet count fall Days 5 – 10 or less than or equal 1 day if there is heparin exposure within the past 30 days. Greater than day 10 or unclear or less than 1 day if heparin exposure within past 30 – 100 days Less than or equal to 1 day with no recent heparin therapy Thrombosis or other sequlae Proven thrombosis, skin necrosis, or other heparin bolus, acute systemic reaction Progressive, recurrent, or silent thrombosis; erythematous skin lesions None Other causes of thrombocytopenia None evident Possible Definite

Table 1: The 4T’s assessment point system.