4T score

Indications

• diagnosis of heparin-induced thrombocytopenia

Procedure

• thrombocytopenia
  • platelet count fall > 50% & nadir > 20,000/uL = 2 points
  • platelet count fall 30-50% or nadir 10,000-19,000/uL = 1 point
• timing of platelet count fall
  • clear onset between days 5-10 of heparin therapy = 2 points
  • onset witbin 1 day of heparin therapy and prior heparin exposure within 30 days = 2 points
  • consistent with onset between days 5-10 of heparin therapy, but not documented (missing platelet count) = 1 point
  • onset after days 10 of heparin therapy = 1 point*
  • onset witbin 1 day of heparin therapy and prior heparin exposure 30-100 days = 1 point*
• thrombosis or other sequellae
  • new thrombosis, skin necrosis or acute systemic reaction after IV bolus of unfractionated heparin = 2 points
  • progressive or recurrent thrombosis, erythematous skin lesions, or suspected thrombosis = 1 point
• other causes for thrombocytopenia identified
  • none = 2 points
  • possible = 1 point

* not included in Online calculator

Interpretation

• maximum score: 8
• 0-3 = low probability
• 4-5 = intermediate probability
• 6-8 = high probability

More general terms

• numerical rating scale (NRS)

Additional terms

• heparin-induced thrombocytopenia; heparin-associated antibody syndrome (HIT)