HIT 4T score is a rating used to help clinicians

Evaluation of pretest clinical score (4 T’s) for the diagnosis of heparin-induced thrombocytopenia in two clinical settings

G K Lo , D Juhl, T E Warkentin, C S Sigouin, P Eichler, A Greinacher

Heparin-induced thrombocytopenia (HIT)

It is a side effect of heparin treatment that causes thrombocytopenia (low platelet count). HIT may be classified into two parts. In most cases, type 1 HIT manifests itself during the first 2 days after being exposed to heparin, and the platelet count returns to normal with continuous heparin treatment. Type 1 HIT is a non-immune disease that develops as a consequence of the direct impact of heparin on the activation of platelet cells.

A type 2 HIT is an immune-mediated disease that usually manifests itself 4-10 days after exposure to heparin and is associated with life- and limb-threatening thrombotic events. Type 2 HIT is more common in women than in men. When the word HIT is used in normal medical practice, it refers to type 2 HIT.

How to Calculate HIT 4T Score

How to Calculate HIT 4T Score

Check for thrombocytopenia, platelet count and nadir.
Check for time required for platelet count to fall.
Check for thrombosis, skin necrosis, or acute systemic reaction.
Review other causes for thrombocytopenia.

HIT 4T Score Calculator

1. Thrombocytopenia
2. Timing of platelet count fall
3. Thrombosis or other sequelae
4. Other causes for thrombocytopenia present


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