© 2003 Fellowship of Postgraduate Medicine
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A complication of hip surgery
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The most likely diagnosis is heparin-induced thombocytopenia (HIT, previously called HIT II), secondary to the prophylactic low molecular weight heparin given perioperatively during orthopaedic surgery. It is caused by immune complex formation, and in some cases results in platelet activation causing thrombosis, as is seen here: heparin induced thrombocytopenia thrombotic syndrome (HITTS). The other main differential diagnosis is idiopathic thromboctytopenic purpura.
The diagnosis of HIT is confirmed by a blood test demonstrating activated IgG antibodies towards heparin complexed to platelet factor 4. Several different platelet release assay methods are available for the detection of the HIT antibody and vary among laboratories. A commonly used technique is a platelet aggregation assay; these are widely available and can assess cross reactivity to other heparin-like agents. Figure 1
illustrates platelet aggregation tracings. A bone marrow aspirate should be performed; this will show normal or increased numbers of platelets and megakaryocytes.
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Figure 1 Normal platelets are | |||||||||
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