Pretest probability of heparin-induced thrombocytopenia (4-T's score)

 

Thrombocytopenia
		Platelet count fall >50 percent AND nadir ≥20,000/microL (2 points)
		Platelet count fall 30 to 50 percent OR nadir 10 to 19,000/microL (1 point)
		Platelet count fall <30 percent OR nadir <10,000/microL (0 points)
Timing of platelet count fall
		Clear onset between days 5 and 10 of heparin exposure, OR platelet count fall at ≤1 day if prior heparin exposure within the last 30 days (2 points)
		Consistent with fall in platelet count at 5 to 10 days, but unclear (eg, missing platelet counts), OR onset after day 10, OR fall ≤1 day with prior heparin exposure within 30 to 100 days (1 point)
		Platelet count fall at <4 days without recent heparin exposure (0 points)
Thrombosis or other sequelae
		Confirmed new thrombosis, skin necrosis, or acute systemic reaction after intravenous unfractionated heparin bolus (2 points)
		Progressive or recurrent thrombosis, non-necrotizing (erythematous) skin lesions, or suspected thrombosis that has not been proven (1 point)
		None (0 points)
Other causes for thrombocytopenia present
		None apparent (2 points)
		Possible (1 point)
		Definite (0 points)

 

Total Criteria Point Count:
 

 

4 T's score interpretation

 

0 to 3 points:	Low probability
4 to 5 points:	Intermediate probability
6 to 8 points:	High probability

 

 

References

1. Lo GK, Juhl D, Warkentin TE, et al. Evaluation of pretest clinical score (4 T's) for the diagnosis of heparin-induced thrombocytopenia in two clinical settings. J Thromb Haemost. 2006 Apr;4(4):759-65. PubMed ID: 16634744