Conventional thrombophilia testing typically involves the determination of deficiencies in antithrombin, protein C, or protein S, and genetic testing for the factor V Leiden (FVL) and prothrombin G20210A variants.3However, despite their widespread use, these tests are critically flawed with limited sensitivity and specificity for VTE, as well as with methodological issues. Here, PROS1 is linked to Rare hereditary thrombophilia.