4 Ts score parameters: |
Thrombocytopenia: |
- PLT decrease >50% AND nadir ≥20,000/microL AND no surgery within preceding 3 days
| 2 points |
- PLT decrease >50% BUT surgery within preceding 3 days OR any combination of PLT fall and nadir that does not fit criteria for 2 or 0 points (eg, 30 to 50% fall or nadir 10,000 to 19,000/microL)
| 1 point |
- PLT decrease <30% OR nadir <10,000/microL
| 0 points |
Timing of onset after heparin exposure: |
- 5 to 10 days OR 1 day if exposure within past 5 to 30 days
| 2 points |
- Probable 5 to 10 days (eg, missing PLT counts) OR >10 days OR <1 day if exposure within past 31 to 100 days
| 1 point |
- ≤4 days without exposure within past 100 days
| 0 points |
Thrombosis or other clinical sequelae: |
- Confirmed new thrombosis, skin necrosis, anaphylactoid reaction, or adrenal hemorrhage
| 2 points |
- Suspected, progressive, or recurrent thrombosis, skin erythema
| 1 point |
| 0 points |
Other cause for thrombocytopenia: |
| 2 points |
| 1 point |
- Probable (eg, DIC, medication, within 72 hours of surgery)
| 0 points |
Interpretation: |
0 to 3 points – Low probability (<1%) |
4 to 5 points – Intermediate probability (approximately 10%) |
6 to 8 points – High probability (approximately 50%) |