Heparin-induced thrombocytopenia (HIT) is a severe complication of heparin therapy with a non-negligible incidence (estimated at 2.6% of unfractionated heparin treatments and 0.2% of low molecular weight heparin treatments). It is generally secondary to the appearance of IgG antibodies directed against the platelet factor 4 (PF4) - heparin complex. These antibodies, once bound to this complex, are likely to activate platelets: the thrombotic risk generated can be potentially fatal.

Inclusion criteria :

• Adult patient (≥ 18 years of age)
• Hospitalized at HUS between 01/01/2009 and 31/12/2019
• Specimen sent to the HUS Hematology Laboratory for biological diagnosis of HIT between 01/01/2009 and 31/12/2019
• Data collected by the CRPV and analyzed by the HIT multidisciplinary group in order to reach a consensus decision on the presence or absence of HIT
• Patient does not object to the reuse of his medical data for scientific research purposes.

Exclusion criteria:

• Patient for whom no test has been performed at the HUS Hematology Laboratory
• Patient for whom no data has been collected by the CRPV
• Patient for whom the HIT group could not confirm or deny the presence of HIT

Adult patient (≥ 18 years of age) hospitalized at HUS between 01/01/2009 and 31/12/2019