Diagnostic Criteria for Heparin-Induced Thrombocytopenia (HIT)

Sponsored Links

Diagnostic Criteria for Heparin-Induced Thrombocytopenia (HIT)

Heparin exposure >5 days
Relative thrombocytopenia: decrease in platelet count by 50% from baseline OR absolute thrombocytopenia: decrease in platelet count to less than 100 to 150 x 10⁹/L
Absence of other causes of thrombocytopenia
Development of new thrombosis, or extension of pre-existing thrombosis, while receiving heparin therapy
Confirmation by laboratory testing
Return to normal platelet count when heparin is discontinued

Serology tests to determine HIT (listed in order of greatest to lowest sensitivity)

Estimating the Pretest Probability of HIT: The "Four T's"

	Points (0, 1, or 2 for Each of 4 Categories: Maximum Possible Score = 8)
	2	1	0
Thrombocytopenia	>50% Platelet fall to nadir >/= 20	30–50% Platelet fall, or nadir 10-19	<30% Platelet fall, or nadir <10
Timing* of onset of platelet fall (or other sequelae of HIT)	Days 5–10, or </= day 1 with recent heparin (past 30 days)	>Day 10 or timing unclear; or <day 1 with recent heparin (past 31–100 days)	<Day 4 (no recent heparin)
Thrombosis or other sequelae	Proven new thrombosis; skin necrosis; or acute systemic reaction after intravenous UFH bolus	Progressive or recurrent thrombosis; erythematous skin lesions; suspected thrombosis (not proven)	None
OTher cause(s) of platelet fall	None evident	Possible	Definite

UFH, Unfractionated heparin

Pretest probability score: 6–8 indicates high; 4–5, intermediate; and 0–3, low.

*First day of immunizing heparin exposure considered day 0.

Related Criteria

Classification of Neutropenia

References:

Warkentin TE, Aird WC, Rand JH. Platelet-endothelial interactions: sepsis, HIT, and antiphospholipid syndrome. Hematology (Am Soc Hematol Educ Program). 2003;:497-519. [Medline]
Warkentin TE, Cook DJ. Heparin, low molecular weight heparin, and heparin-induced thrombocytopenia in the ICU. Crit Care Clin. 2005 Jul;21(3):513-29. [Medline]