In general, a negative iodine test is also the result of an iodine allergy test, or a skin sensitization test for contrast agents such as iodohexol. A negative test means that there is no allergic reaction to iodine or its preparations, and iodine-containing preparations can be applied. The iodine test is often used in the clinic, especially for enhanced CT and MRI examinations, and is performed in the same way as the general drug sensitization test. Only after the iodine test is negative can iodine-containing contrast agents be used for further examination. However, it should be noted that a small number of patients with negative allergy test have allergic reactions during the imaging, so first-aid drugs should be prepared during the imaging. In addition, it is recommended that patients go to regular hospitals for iodine allergy test, iodinol and other contrast agents for skin allergy test, to avoid operation irregularities leading to errors in the results.