The 4T’s Score is a clinical prediction tool used to estimate the probability that a patient’s thrombocytopenia is due to Heparin-Induced Thrombocytopenia (HIT) rather than other causes. It is widely used because it’s simple, bedside-friendly, and helps decide whether to stop heparin and send HIT antibody testing.
Short article: What is the 4T’s Score?
4T’s Score (Heparin-Induced Thrombocytopenia)
Bedside tool to estimate the pre-test probability of HIT based on thrombocytopenia, timing, thrombosis and other causes.
4T’s • Score 0–8
4T’s Components
Select the single most appropriate option in each category.
Clinical decision support only.
This calculator does not diagnose HIT and does not replace clinical judgement,
local guidelines or specialist consultation.
1. Thrombocytopenia (platelet fall)
Use percentage fall from peak platelet count and nadir value.
2. Timing of platelet count fall
Relate onset of platelet fall to first exposure of heparin in this episode.
3. Thrombosis or other sequelae
Include new thrombosis, skin lesions or systemic reactions temporally related to heparin.
4. Other causes of thrombocytopenia
Consider sepsis, medications, DIC, recent surgery, bone marrow disease, etc.
