Heparin-induced thrombocytopenia (HIT) is a serious adverse reaction to heparin, characterized by a decrease in platelet count and the presence of heparin-dependent IgG antibodies. A study compared unfractionated heparin (UH) and low-molecular-weight heparin (LMWH) in 665 patients undergoing hip surgery for thrombosis prophylaxis. Platelet counts were monitored daily, and HIT was defined as a platelet count below 150,000 per cubic millimeter five or more days after heparin therapy, along with a positive test for heparin-dependent IgG antibodies. A subgroup of 387 patients was tested for these antibodies regardless of platelet counts. The study found that HIT occurred in 2.7% of patients treated with UH and 0% with LMWH. Eight of nine patients with HIT also had thrombotic events, including venous and arterial thrombosis. HIT was strongly associated with thrombotic complications, with an odds ratio of 36.9. Patients treated with UH had a higher frequency of HIT and heparin-dependent IgG antibodies compared to those treated with LMWH. HIT was a significant risk factor for thrombotic events, particularly venous thrombosis. The study also found that early postoperative thrombocytopenia was common but not related to HIT. HIT was more common in patients treated with UH, and the presence of heparin-dependent IgG antibodies was more frequent in these patients. However, some patients with HIT did not have thrombocytopenia, possibly due to variability in platelet reactivity to the antibodies. The study concluded that HIT and associated thrombotic complications are more common with UH than with LMWH. LMWH has advantages over UH, including less need for anticoagulant monitoring and a greater therapeutic index. However, LMWH is more expensive. HIT is not indicated for treatment with LMWH due to cross-reactivity. The study highlights the importance of using LMWH in patients at risk for HIT to reduce the risk of thrombotic complications.Heparin-induced thrombocytopenia (HIT) is a serious adverse reaction to heparin, characterized by a decrease in platelet count and the presence of heparin-dependent IgG antibodies. A study compared unfractionated heparin (UH) and low-molecular-weight heparin (LMWH) in 665 patients undergoing hip surgery for thrombosis prophylaxis. Platelet counts were monitored daily, and HIT was defined as a platelet count below 150,000 per cubic millimeter five or more days after heparin therapy, along with a positive test for heparin-dependent IgG antibodies. A subgroup of 387 patients was tested for these antibodies regardless of platelet counts. The study found that HIT occurred in 2.7% of patients treated with UH and 0% with LMWH. Eight of nine patients with HIT also had thrombotic events, including venous and arterial thrombosis. HIT was strongly associated with thrombotic complications, with an odds ratio of 36.9. Patients treated with UH had a higher frequency of HIT and heparin-dependent IgG antibodies compared to those treated with LMWH. HIT was a significant risk factor for thrombotic events, particularly venous thrombosis. The study also found that early postoperative thrombocytopenia was common but not related to HIT. HIT was more common in patients treated with UH, and the presence of heparin-dependent IgG antibodies was more frequent in these patients. However, some patients with HIT did not have thrombocytopenia, possibly due to variability in platelet reactivity to the antibodies. The study concluded that HIT and associated thrombotic complications are more common with UH than with LMWH. LMWH has advantages over UH, including less need for anticoagulant monitoring and a greater therapeutic index. However, LMWH is more expensive. HIT is not indicated for treatment with LMWH due to cross-reactivity. The study highlights the importance of using LMWH in patients at risk for HIT to reduce the risk of thrombotic complications.