Which type of contrast is less likely to cause an allergic reaction?

Nonionic contrast is less likely to cause an allergic reaction because it has a lower osmolality compared to ionic and high-osmolar contrast agents. This is significant because lower osmolality reduces the potential for adverse effects and reactions in patients. The chemical structure of nonionic contrast agents is designed to minimize the ionic content and prevent the creation of hyperosmolar conditions, which can lead to a higher incidence of allergic reactions and side effects.

Patients with a history of allergies are often cited as having fewer reactions with nonionic agents. The improved safety profile of nonionic contrast allows for a smoother administration process and is typically preferred in clinical settings, especially for patients who might be at higher risk for allergic responses.

These characteristics contribute to the overall preference among radiology departments for using nonionic contrast agents whenever possible.