What is the most likely factor abnormality found in a 27 year-old male nonsmoker diagnosed with upper extremity venous thrombosis?

In the context of upper extremity venous thrombosis, particularly in a young, nonsmoking male, the most likely factor abnormality associated with the condition is Factor V. This is primarily related to Factor V Leiden, a common genetic mutation that causes resistance to activated protein C, leading to an increased risk of venous thrombosis.

Factor V Leiden mutation is particularly significant because it can lead to thrombosis even in patients who do not have traditional risk factors, such as smoking, prolonged immobility, or a prior history of thromboembolic events. In young individuals with thrombosis in unusual locations, like the upper extremities, thrombophilia screening often reveals abnormalities such as Factor V Leiden. It is one of the more prevalent inherited thrombophilias, making it a key consideration for this clinical scenario.

Other factor abnormalities like Factor VIII, Factor I, and Factor X are associated with different conditions or have less direct relevance to the thrombosis mechanism in this case, making them less likely to explain the patient's diagnosis.