Final answer:
An allergy to shellfish requires further screening before a CT scan with IV contrast as it can trigger an allergic reaction due to iodine in the contrast dye.
Step-by-step explanation:
The nurse should identify an allergy to shellfish as the finding that requires further screening before a patient undergoes a CT scan with IV contrast agent. The contrast dye used in CT scans may contain iodine, which can cause a reaction in patients with shellfish allergies due to the presence of natural iodine in shellfish. Therefore, it is crucial to ascertain any allergies to shellfish prior to administering a contrast agent. While a history of hypertension, a previous CT scan without contrast, and a family history of diabetes are all valuable pieces of health history, they do not have the same immediate potential risk associated with the administration of a contrast dye as a shellfish allergy does.