The first step a physician is likely to take in the diagnosis of a food allergy is to complete a physical examination and create a detailed medical history, including the dietary history of the patient. The history may include the following information:

• Timing of the reaction (e.g., whether the reaction occurred within an hour after eating)
  
  
• Whether the reaction is always associated with a certain food
  
  
• How much of the food was consumed, because the severity of a reaction may relate to the amount of food consumed
  
  
• Whether treatment for a reaction was successful (e.g., if taking antihistamines relieved the symptoms)

While these first steps are often inconclusive, they can create a better idea of where to proceed with further testing. There are several additional evaluation options available to physicians.

• Skin test. This test involves pricking, scratching or injecting food extracts into the patient’s skin. The skin will react with redness and swelling for those extracts capable of eliciting an allergic reaction when consumed. This type of test does not provide results that are 100 percent accurate, however, and results will vary depending on the food being tested.
  

  
  

• RAST (radioallergosorbent test). This type of blood test allows a laboratory to directly examine a blood sample for antibodies that correspond to specific foods or food additives. While less sensitive than a skin test, it can be used on individuals who have reactions too severe for a skin test.
  
  
• Elimination diet. This involves removing suspect foods from a patient’s diet to see if the allergic reactions persist. This trial-and-error approach often takes weeks for results, but it can be effective at pinpointing and removing a problem food.
  
  
• Oral food challenge. This is considered the most effective way of determining the cause of a food allergy because it supplies the most convincing results. Different foods are placed within capsules to hide their identity. The patient consumes the capsules and the physician looks for signs of an allergic reaction. This type of test is time-consuming and difficult. It is often reserved to confirm suspicions that a patient's symptoms are not caused by a food allergy.