Q: How HIT Expert Probability (HEP) Score differs from 4 T's score in the management of Heparin Induced Thrombocytopenia (HIT)?


Answer: 

In HEP score, points are subtracted or added depending on bleeding or presence of devices or other causes of Thrombocytopenia. It is an excellent measuring score but may be cumbersome. A HEP score cut-off of 2 would lead to 100% sensitivity and 60% specificity while a cut-off of 5 would maximize sensitivity/specificity at 86% and 88%, respectively,

Clinical Feature	Presentation	Score
Magnitude of fall in platelet count (measured from peak to nadir since heparin exposure)	< 30%	-1
	30-50%	+1
	>50%	+3
Timing of fall in platelet count	For patients in whom typical onset HIT is suspected:
	Fall begins < 4 days after heparin exposure	-2
	Fall begins 4 days after heparin exposure	+2
	Fall begins 5-10 days after heparin exposure	+3
	Fall begins 11-14 days after heparin exposure	+2
	Fall begins > 14 days after heparin exposure	-1
	For patients with previous heparin exposure in the last 100 days in whom rapid onset HIT is suspected:
	Fall begins < 48 hours after heparin exposure	+2
	Fall begins > 48 hours after heparin exposure	-1
Nadir platelet count	≤ 20 × 109 L−1	-2
	> 20 × 109 L−1	+2
Thrombosis (select no more than one)	For patients in whom typical onset HIT is suspected:
	New VTE or ATE > 4 days after heparin exposure	+3
	Progression of pre-existing VTE/ATE while receiving heparin	+2
	For patients in whom rapid onset HIT is suspected:
	New VTE or ATE after heparin exposure	+3
	Progression of pre-existing VTE /ATE while receiving heparin	+2
Skin necrosis	Skin necrosis at subcutaneous heparin injection sites	+3
Acute systemic reaction	Acute systemic reaction after intravenous heparin bolus	+2
Bleeding	Presence of bleeding, petechiae, or extensive bruising	-1
Other causes of thrombocytopenia (select all that apply)	Presence of a chronic thrombocytopenic disorder	-1
	Newly initiation non-heparin med known to cause thrombocytopenia	-2
	Severe infection	-2
	Severe DIC (fibrinogen < 100 mg/dL and D-dimer > 5 mcg/ml)	-2
	Indwelling intra-arterial device (IABP, VAD, ECMO)	-2
	Cardiopulmonary bypass within previous 96 hrs	-1
	No other apparent cause	+3
VTE=venous thromboembolism; ATE=arterial thromboembolism; DIC=disseminated intravascular coagulation

References: 

1. Cuker A, Arepally G, Crowther MA, et al. The HIT Expert Probability (HEP) Score: a novel pre-test probability model for heparin-induced thrombocytopenia based on broad expert opinion. J Thromb Haemost 2010; 8:2642. 

2. Joseph L, Gomes MP, Al Solaiman F, et al. External validation of the HIT Expert Probability (HEP) score. Thromb Haemost 2015; 113:633.