In evaluating a potential allergic reaction to a vaccine, a physician will take a medical history and perform a physical examination. The physician may also take the following steps:

• Determine if the nature and timing of reactions are consistent with anaphylaxis.
  
  
• Obtain a history of similar reactions to the vaccine, or to other similar vaccines.
  
  
• Obtain a history of allergic reactions to foods.
  
  
• Determine if the patient will need additional doses of the vaccine or a substitute in the future. If not, the patient may simply be diagnosed as allergic to the vaccine, and no further treatment will be required. However, the patient may be more extensively tested to ensure an accurate diagnosis and to prevent exposure to other vaccines or foods that may cross-react with the allergen.

A physician may also perform allergy skin tests to confirm an allergy to a vaccine. Such testing must be done under close supervision and in a medical facility, as there is a small chance that the test itself could induce anaphylactic shock.