PROS1 and hematocrit: The first HT condition was described by Egberg in 1965 when he discussed the inherited risk of VTE in patients with a deficiency in antithrombin III [8]. In 1981, Griffin et al. [9] reported an increased risk of VTE in patients with decreased protein C levels, which was followed by similar findings in patients with decreased protein S and mutations in the factor V Leiden gene [10-12].