Our hypothesis was that the frequencies of seroconversion of IgG-class anti-PF4/heparin would be reduced in patients receiving fondaparinux, and even in those receiving LMWHs, and we focused on the relationship between seroconversion of these antibodies and the occurrence of symptomatic DVT under different anti-thrombotic prophylaxis therapeutics. This evidence concerns the gene PF4 and deep vein thrombosis.