Which of the following is not a step in the primary assessment of a trauma patient?

The primary assessment of a trauma patient is designed to quickly identify and address any life-threatening conditions. This assessment typically includes evaluating the airway and breathing to ensure the patient can adequately ventilate, assessing circulation to look for signs of shock or hemorrhage, and identifying disabilities which can provide insight into the patient's neurological status.

Checking for past medical history, while important for overall patient care and treatment planning, is not part of the immediate primary assessment. This step is usually conducted later when time allows and the immediate life threats have been addressed. Therefore, when considering the focus and structure of the primary assessment, understanding that it revolves around the "ABCD" approach—Airway, Breathing, Circulation, and Disability—clearly indicates that past medical history does not fit into this urgent evaluation framework.