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Table 1 4T’s, a pretest scoring system used in the clinical diagnosis of HIT.

From: Apixaban for treatment of confirmed heparin-induced thrombocytopenia: a case report and review of literature

Clinical feature

2 points

1 point

0 point

Thrombocytopenia

Platelet decrease >50% from baseline platelet nadir >20,000

Platelet decrease of 30–50% platelet nadir 10,000–19,000

Platelet decrease <30% platelet nadir <10,000

Timing of platelet decrease

5–10 days after heparin exposure OR ≤1 day (if exposed to heparin within 30 days)

Likely 5–10 days (incomplete evidence) OR onset after day 10 OR ≤1 day (if exposed to heparin within 30–100 days)

≤4 days without recent exposure

Thrombosis or other sequelae

New and confirmed thrombosis skin necrosis anaphylactic reaction to IV unfractionated heparin

Progressive/recurrent thrombosis non-necrotizing skin lesions unconfirmed thrombosis

None

Other etiologies for thrombocytopenia

None

Possible

Definite

  1. High probability of HIT: 6–8 points; intermediate probability of HIT: 4–5 points; low probability of HIT: ≤3 points; recommended to discontinue heparin products and start non-heparin anticoagulant with score of ≥4; HIT: heparin-induced thrombocytopenia
Adapted from Lo et al. [13]