This study investigates the frequency and clinical outcomes of heparin-induced thrombocytopenia (HIT) in patients treated with low-molecular-weight heparin (LMWH) or unfractionated heparin (UFH) after hip surgery. The researchers conducted a randomized, double-blind clinical trial involving 665 patients, comparing the two types of heparin. HIT was defined as a platelet count below 150,000 per cubic millimeter five or more days after heparin therapy, plus a positive test for heparin-dependent IgG antibodies. Key findings include: - HIT occurred in 2.7% of patients receiving UFH, compared to 0% of those receiving LMWH. - HIT was strongly associated with thrombotic events, particularly venous thrombosis. - In the subgroup of 387 patients tested for heparin-dependent IgG antibodies, 20 patients tested positive, with a higher frequency in those receiving UFH. - HIT was a significant risk factor for thrombotic complications, with an overall frequency of 2.4% associated with thrombosis. The study suggests that HIT and its associated thrombotic complications are relatively common adverse effects of heparin therapy, and that LMWH is associated with a lower risk of HIT and thrombotic events compared to UFH. However, LMWH is not indicated for treating HIT due to cross-reactivity between the two forms of heparin.This study investigates the frequency and clinical outcomes of heparin-induced thrombocytopenia (HIT) in patients treated with low-molecular-weight heparin (LMWH) or unfractionated heparin (UFH) after hip surgery. The researchers conducted a randomized, double-blind clinical trial involving 665 patients, comparing the two types of heparin. HIT was defined as a platelet count below 150,000 per cubic millimeter five or more days after heparin therapy, plus a positive test for heparin-dependent IgG antibodies. Key findings include: - HIT occurred in 2.7% of patients receiving UFH, compared to 0% of those receiving LMWH. - HIT was strongly associated with thrombotic events, particularly venous thrombosis. - In the subgroup of 387 patients tested for heparin-dependent IgG antibodies, 20 patients tested positive, with a higher frequency in those receiving UFH. - HIT was a significant risk factor for thrombotic complications, with an overall frequency of 2.4% associated with thrombosis. The study suggests that HIT and its associated thrombotic complications are relatively common adverse effects of heparin therapy, and that LMWH is associated with a lower risk of HIT and thrombotic events compared to UFH. However, LMWH is not indicated for treating HIT due to cross-reactivity between the two forms of heparin.