Heparin-induced thrombocytopenia (HIT) is a life-threatening complication of exposure to heparin (ie, unfractionated heparin, low molecular weight [LMW] heparin) that occurs in up to 5 percent of patients exposed, regardless of the dose, schedule, or route of administration. HIT results from an autoantibody directed against platelet factor 4 (PF4) in complex with heparin. HIT antibodies activate platelets and can cause catastrophic arterial and venous thrombosis, with a mortality rate as high as 20 percent, although with improved recognition and early intervention, mortality rates below 2 percent have been reported.
Here we discuss the prevention and management of HIT. The clinical presentation and diagnosis of HIT are discussed separately. (See "Clinical presentation and diagnosis of heparin-induced thrombocytopenia".)
IMMEDIATE DISCONTINUATION OF HEPARIN
Presumptive diagnosis of HIT — We always consider clinical and laboratory evidence in evaluating patients for heparin-induced thrombocytopenia (HIT). However, definitive laboratory data (ie, immunoassay and/or functional assay for HIT antibodies) may not be available for several days. Thus, we make a presumptive diagnosis of HIT based on clinical findings and immediately available laboratory data.
Clinicians, particularly those who have less familiarity with HIT, should involve the consulting hematologist as early as possible in determining the likelihood of HIT because a presumptive diagnosis of HIT carries management implications (eg, discontinuation of heparin, administration of a non-heparin anticoagulant). Not diagnosing HIT when it is present or mistakenly diagnosing HIT when it is absent are both associated with significant risks (eg, life-threatening thrombosis if a diagnosis is missed; life-threatening bleeding and high cost of presumptive treatment with a non-heparin anticoagulant if an incorrect diagnosis is made).
The 4 T's score (calculator 1) is an easy-to-use score that quantifies the clinical findings associated with HIT (eg, degree of Thrombocytopenia, Timing, Thrombotic events or sequelae, alternative causes of thrombocytopenia). The 4 T's score should be used as a guide for clinicians and should not substitute for clinical judgement .