This is something your doctor decides when he orders the CT. These can be done both with and without contrast. Most often times allergic reactions do not occur.

IV contrast may or may not be used for CT scan of the lungs, depending on if your provider ordered it. Most contrast reactions are mild, such as itching and hives. However, rarely, a severe reaction can occur. Food allergies, such as shellfish allergy, have nor correlation with having a contrast reaction.