Why is it important to gather information about the casualty’s medical history?

Gathering information about the casualty’s medical history is crucial because it provides critical information for treatment. Understanding a person's previous medical conditions, allergies, medications, and any chronic illnesses can significantly influence the care provided. For example, knowing about allergies can prevent administering a medication that may cause an adverse reaction. Additionally, knowledge of pre-existing conditions can guide interventions and affect choices in immediate care. This information allows responders to tailor their treatment strategies effectively, increasing the chances of a safe and successful outcome for the casualty.

The other options, while they may have their own relevance in certain contexts, do not reflect the immediate necessity and implications of medical history in a treatment scenario as directly as option B does.