Heparin-induced thrombocytopenia risk factors

	Heparin-induced thrombocytopenia
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor-In-Chief: Cafer Zorkun, M.D., Ph.D. [2], Aric C. Hall, M.D., [3] Shyam Patel [4]

Overview

Heparin-induced thrombocytopenia is diagnosed when the platelet count falls by > 50% typically after 5-10 days of heparin therapy. Increased risks for heparin-induced thrombocytopenia depends on type of heparin (unfractionated heparin > low molecular weight heparin), duration of therapy, females and type of patients (commoner in surgical patients that require large amount of heparin)

Adverse risk factors include:^[1]

Duration of heparin treatment: A long duration of heparin expsosure, such as 2 weeks, is associated with the greatest risk.
Type of heparin: unfractionated heparin (UFH) has a greater risk than low molecular weight heparin (LMWH.
Type of patient: surgical patients are at higher risk than medical; cardiac surgical patients have the highest risk of all.^[2] This is though to be related to differences in basal level of circulating platelet factor 4 (PF4) and platelet activation in these various populations.
There is no increase in risk of HIT with genetic risk factors for thrombosis such as factor V Leiden, prothrombin gene mutation, methylenetetrahydrofolate reductase (MTHFR) polymorphism and platelet-receptor polymorphisms.
Sex: Females have a higher risk than males. The odds ratio (OR) is 2.4:1.^[2]
Race: African Americans are more prone to HIT than Caucasians.^[2]

Protective risk factors include:

Type of warfarin: Use of low molecular weight heparin such as enoxaparin carries a lower risk for HIT.
Type of patient: Pediatric or obstetric patients have a lower risk for HIT than medical or surgical patients.

↑ Warkentin TE, Sheppard JA, Sigouin CS, Kohlmann T, Eichler P, Greinacher A. Gender imbalance and risk factor interactions in heparin-induced thrombocytopenia. Blood 2006;108:2937-41. PMID 16857993.
↑ ^2.0 ^2.1 ^2.2 Lee GM, Arepally GM (2013). "Diagnosis and management of heparin-induced thrombocytopenia". Hematol Oncol Clin North Am. 27 (3): 541–63. doi:10.1016/j.hoc.2013.02.001. PMC 3668315. PMID 23714311.