2 points 1 point 0 points Thrombocytopenia Pattern most suggestive of HITT: >50% drop AND Nadir >20,000 Patterns less suggestive of HITT: 30 - 50% drop OR Nadir 10,000 - 19,000 Patterns arguing against HITT: < 30% drop OR Nadir <10,000 Timing Fall 5 - 10 days after starting heparin OR Fall 1 day after starting heparin in patient exposed within past month - Platelet fall after >10 days OR - Fall 1 day after starting heparin & exposure to heparin in past 30 - 100 days OR - Fall possibly 5 - 10 days after starting heparin, but incomplete data Platelet fall <5 days without exposure to heparin in past 100 days Thrombosis New thrombosis (arterial or venous) OR Skin necrosis at site of heparin injection OR Anaphylactoid reaction to IV heparin bolus OR Adrenal hemorrhage Recurrent or progressive venous thrombosis OR Suspected thrombosis awaiting imaging OR Erythematous skin lesion at site of heparin injection No thrombus oTher explanation? None Possible Definite 4T score to risk - stratify for heparin - induced thrombocytopenia (HITT) Add up total score Score 0 - 3 Low risk <1% probability of HITT Score 4 - 5 Intermediate risk 10 - 15% probability of HITT Score 6 - 7 High risk 50 - 60% probability of HITT interpretation