Before injecting a contrast agent, a radiographer should:

Checking for allergies to contrast media is a crucial step before injecting a contrast agent. This is important because some patients may have a history of allergic reactions to iodine-based contrast materials or other components found in contrast agents. Reactions can range from mild (such as hives or itching) to severe anaphylactic reactions, which can be life-threatening. Knowing the patient's allergy history allows the radiographer to take necessary precautions, such as using an alternative contrast agent or premedication, to prevent any adverse effects.

In this context, knowing the patient's blood type, while important in certain medical settings, is not relevant to the administration of contrast media. Reviewing the patient's diet is not typically necessary unless specific dietary restrictions are advised prior to certain imaging studies. Assessing vital signs can be part of patient monitoring but does not address the risk of allergic reactions specifically related to contrast administration. Therefore, checking for allergies directly addresses a critical safety concern in radiographic procedures involving contrast agents.