Hematology
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A 38-year-old morbidly obese male (BMI > 50 kg/m(2)) presents for an elective gastric bypass surgery. He has no personal or family history of venous thromboembolism or hypercoaguability. You are asked by his primary team whether he should receive a retrievable inferior vena cava filter preoperatively for venous thromboembolism prophylaxis.
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Review
Heparin-induced thrombocytopenia: when a low platelet count is a mandate for anticoagulation.
Heparin-induced thrombocytopenia (HIT) is an immune-mediated disorder caused by the development of antibodies to platelet factor 4 (PF4) and heparin. The thrombocytopenia is typically moderate, with a median platelet count nadir of approximately 50 to 60 x 10(9) platelets/L. Severe thrombocytopenia has been described in patients with HIT, and in these patients antibody levels are high and severe clinical outcomes have been reported (eg, disseminated intravascular coagulation with microvascular thrombosis). ⋯ Alternative agents that have been used effectively in patients with HIT include lepirudin, argatroban, bivalirudin, and danaparoid, although the last agent is not available in North America. Fondaparinux has been used in a small number of patients with HIT and generally appears to be safe. Warfarin therapy should not be initiated until the platelet count has recovered and the patient is systemically anticoagulated, and vitamin K should be administered to patients receiving warfarin at the time of diagnosis of HIT.
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Telomeres, repeat sequences at the ends of chromosomes, are protective chromosomal structures highly conserved from primitive organisms to humans. Telomeres inevitably shorten with every cell cycle, and telomere attrition has been hypothesized to be fundamental to normal senescence of cells, tissues, and organisms. Molecular mechanisms have evolved to maintain their length and protective function; telomerase (TERT) is a reverse transcriptase enzyme that uses an RNA molecule (TERC) as the template to elongate the 3' ends of telomeres. ⋯ Additionally, telomere defects associate with predisposition to hematologic malignancy and epithelial tumors. Telomere erosion is abnormally rapid in patients with mutations in telomerase genes but also after hematopoietic stem cell transplant, and telomeres are naturally shorter in older individuals-all conditions associated with higher rates of malignant diseases. In human tissue culture, short telomeres produce end-to-end chromosome fusion, nonreciprocal translocations, and aneuploidy.
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Erythrocytosis results when there is an increased red cell mass and thus an increased hemoglobin. The causes can be divided into primary intrinsic defects of the erythroid progenitor cell and secondary defects, where factors external to the erythroid compartment are responsible. Both can then be further divided into congenital and acquired categories. ⋯ Having eliminated the common entity polycythemia vera, further direction for investigation is guided by the erythropoietin level. Clinical consequences of the various erythrocytoses are not clear, but in some groups thromboembolic events have been described in young patients. Evidence is lacking to define best management, but aspirin and venesection to a target hematocrit should be considered.
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The main reason for the increased risk of thromboembolism in pregnancy is hypercoagulability, which has likely evolved to protect women from the bleeding challenges of miscarriage and childbirth. Women are at a 4- to 5-fold increased risk of thromboembolism during pregnancy and the postpartum period compared with when they are not pregnant. Eighty percent of the thromboembolic events in pregnancy are venous, with an incidence of 0.49 to 1.72 per 1000 pregnancies. ⋯ At the time of delivery, anticoagulation should be manipulated to reduce the risk of bleeding complications while minimizing the risk of thrombosis. There are no large trials of anticoagulants in pregnancy, and recommendations are based on case series, extrapolations from nonpregnant patients and the opinion of experts. Nonetheless, anticoagulants are believed to improve the outcome of pregnancy for women who have, or have had, VTE.