Thromb Haemostasis
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Two unrelated patients belonging to two Italian kindreds with a history of thrombotic manifestations were found to have a double heterozygous defect of factor V (F. V), namely type I quantitative F. V defect and F. ⋯ V Leiden mutation also in patients with the lowest values of APC-SR. It is to be hoped that no patient gets a diagnosis of homozygous F. V Leiden mutation based on the APC-resistance test, especially when the basal clotting tests, i.e., PT and aPTT; are borderline or slightly prolonged.