The first step in diagnosing any condition is likely to be a physical examination. When allergies are suspected, the physician will pay close attention to the patient’s ears, eyes, nose, throat, chest and skin. A pulmonary function test may be used to measure how effectively the patient exhales air from the lungs. X-rays of the lungs or sinuses may also be performed.  

A detailed medical history will also be taken. The physician will inquire as to whether any allergies have been diagnosed in the past. This is significant because a person who is allergic to one substance has a greater chance of being allergic to another substance. In addition, different substances may be chemically similar, triggering an allergic reaction. A list of current medications will be collected as well.

Family medical history is also a factor. If one parent has allergies, there is a 50 percent chance of a child developing allergies, according to the American Academy of Allergy, Asthma and Immunology. If both parents have allergies, this risk jumps to 75 percent.

Physicians will also ask questions about the patient’s lifestyle at home, work or school. This information will further help the physician pinpoint the allergens causing the patient’s allergic reactions.

The primary treatment for any allergy is avoidance – refraining from any contact with the triggering allergen. Because of this, the diagnosis of an allergy involves identifying the specific allergen that triggers the patient’s allergic reaction. Tests that may be used for this purpose include:

• Skin test. This test introduces various allergens to the patient’s skin in specific areas. If redness or swelling occurs in an area, it usually indicates that the patient is allergic to that substance. This type of test does not provide results that are 100 percent accurate and is not usually appropriate for people with certain skin conditions.
  
  

  

   
• RAST (radioallergosorbent test). This blood test allows a laboratory to directly test a blood sample for antibodies that correspond to specific allergens. While less sensitive than a skin test, it can be used on individuals who have reactions too severe to risk the exposure to the allergen required for skin testing. A RAST test is often used to determine sensitivity to food allergies.
  
  
• Elimination Diet. Used in the diagnosis of food allergies, 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 a problem food.
  
  
• Oral food challenge. This is considered the most accurate 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.

Some people turn to complementary and alternative medicine (CAM) allergy tests as an alternative approach to diagnosing allergies. These tests are often unproven and have not shown efficacy in clinical trials. A patient may want to seek a second opinion if a physician suggests one of these tests:

• Cytotoxicity blood test
• Applied kinesiology
• Subcutaneous or sublingual provocation testing
• Neutralization testing
• Electroacupuncture biofeedback
• Urine autoinjection
• Skin titration (Rinkel method)
• Candidiasis allergy theory
• Basophil histamine release
• ELISA/ACT (not to be confused with ELISA, which is often used to test for autoimmune diseases and sometimes for allergies)