4Ts Score with tips and tricks
| 4Ts Score Component . | Tips and tricks . |
|---|---|
| Thrombocytopenia 2: Platelet count fall >50% and nadir ≥20 1: Platelet count fall 30%-50% or nadir 10-19 0: Platelet count fall <30% or nadir <10 | Calculate using the peak platelet count after heparin was started. |
| Patients do not have to be thrombocytopenic to earn points. If the peak platelet count is high enough, the platelet count can decline significantly to meet score criteria and still be in the normal range. | |
| Timing of platelet count fall 2: Clear onset between days 5-10 or fall ≤1 day (prior heparin exposure within 30 days) 1: Consistent with days 5-10 fall but not clear; onset after day 10 or fall ≤1 day (prior heparin exposure 30-100 days ago) 0: Fall <4 days without recent exposure | Calculate based on the first day of consistent platelet count fall. |
| In cardiovascular surgery, platelet count fall is often “biphasic,” where the platelet count declines due to surgery, rebounds, and then declines again due to HIT (Figure 1). | |
| A fall ≤1 day after heparin exposure is due to preformed anti-PF4/heparin antibodies that continue to circulate after a recent heparin exposure. A fall after 5 days occurs because that is the time it takes to develop new IgG antibodies after heparin exposure. | |
| Thrombosis or other sequelae 2: New thrombosis or skin necrosis; acute systemic reaction post-IV heparin bolus 1: Progressive or recurrent thrombosis; nonnecrotizing skin lesions, suspected thrombosis (not proven) 0: None | Points only for thrombosis that occurs or progresses after heparin exposure and while the platelets are declining (or shortly before), not thrombosis that occurred well before heparin exposure and platelet decline. |
| Other causes of thrombocytopenia 2: None apparent 1: Possible 0: Definite | This variable most frequently contributes to interprovider variation.8 Consider using the other causes of thrombocytopenia included in the HEP Score39 as a guide: chronic thrombocytopenia, newly initiated nonheparin medication known to cause thrombocytopenia, severe infection, severe DIC, indwelling intra-arterial device, CPB within 96 hours. |
| 4Ts Score Component . | Tips and tricks . |
|---|---|
| Thrombocytopenia 2: Platelet count fall >50% and nadir ≥20 1: Platelet count fall 30%-50% or nadir 10-19 0: Platelet count fall <30% or nadir <10 | Calculate using the peak platelet count after heparin was started. |
| Patients do not have to be thrombocytopenic to earn points. If the peak platelet count is high enough, the platelet count can decline significantly to meet score criteria and still be in the normal range. | |
| Timing of platelet count fall 2: Clear onset between days 5-10 or fall ≤1 day (prior heparin exposure within 30 days) 1: Consistent with days 5-10 fall but not clear; onset after day 10 or fall ≤1 day (prior heparin exposure 30-100 days ago) 0: Fall <4 days without recent exposure | Calculate based on the first day of consistent platelet count fall. |
| In cardiovascular surgery, platelet count fall is often “biphasic,” where the platelet count declines due to surgery, rebounds, and then declines again due to HIT (Figure 1). | |
| A fall ≤1 day after heparin exposure is due to preformed anti-PF4/heparin antibodies that continue to circulate after a recent heparin exposure. A fall after 5 days occurs because that is the time it takes to develop new IgG antibodies after heparin exposure. | |
| Thrombosis or other sequelae 2: New thrombosis or skin necrosis; acute systemic reaction post-IV heparin bolus 1: Progressive or recurrent thrombosis; nonnecrotizing skin lesions, suspected thrombosis (not proven) 0: None | Points only for thrombosis that occurs or progresses after heparin exposure and while the platelets are declining (or shortly before), not thrombosis that occurred well before heparin exposure and platelet decline. |
| Other causes of thrombocytopenia 2: None apparent 1: Possible 0: Definite | This variable most frequently contributes to interprovider variation.8 Consider using the other causes of thrombocytopenia included in the HEP Score39 as a guide: chronic thrombocytopenia, newly initiated nonheparin medication known to cause thrombocytopenia, severe infection, severe DIC, indwelling intra-arterial device, CPB within 96 hours. |
Each of the 4 components of the 4Ts Score are listed: thrombocytopenia, timing of platelet count fall, thrombosis and other sequelae, and other causes of thrombocytopenia. The point value and its corresponding criteria are listed below each component. In the column to the right of each component are tips and tricks to inform accurate calculation. A total score of 0-3 corresponds with a low risk, 4-5 with an intermediate risk, and ≥6 with a high risk of HIT.