Diagnosing Food Allergies: Keeping Track and Getting Answers

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Wondering whether to grab that handful of peanuts? Not certain you should add that dash of milk to your coffee? If you experience adverse reactions to these foods or others, you might have a food allergy. Unlike food intolerances, which also cause discomfort, food allergies result from a flawed immune system response. Here's what happens: Your immune system identifies a food as dangerous and releases antibodies known as immunoglobulin E (IgE) to strike back and destroy the threat. The next time you eat the trigger food – even a tiny bit - the IgE antibodies tell your immune system to release histamine (a protein), which sets off an allergic reaction.

Common Food Allergies and Symptoms

Most food allergies result from proteins found in:
  • eggs
  • fish
  • milk
  • peanuts
  • tree nuts (pecans, walnuts)
  • shellfish (crab, lobster, shrimp).
Symptoms of food allergies range from moderate to severe to life-threatening. Unlike drug allergies, which can trigger symptoms long after the exposure, food allergies usually elicit a reaction within minutes or hours of that first bite. More moderate symptoms include:
  • abdominal cramping
  • diarrhea
  • dizziness or fainting
  • eczema (dry, red and itchy skin rash)
  • itchy skin or hives
  • swollen face, lips, throat, tongue or other parts of the body
  • tingling or numbness of the mouth.
Over-the-counter or prescribed antihistamines may relieve some of these symptoms (itching and hives), but they cannot cure the allergy.
 
Severe allergic reactions require immediate medical attention and fall under a systemic (whole-body) and life-threatening condition known as anaphylaxis. Symptoms of anaphylaxis include:
  • abdominal cramping
  • bluing of the skin
  • confusion
  • difficulty breathing
  • dizziness
  • irregular or fast heartbeat
  • swollen throat (or difficulty swallowing).
If you experience any of these symptoms, call for help right away and do not attempt to drive. Healthcare providers will evaluate your signs and administer the appropriate treatment – CPR, epinephrine (adrenaline), IV fluids or antihistamines.

Diagnosing Food Allergies

Diagnosing a food allergy can take time or happen quickly. At your first visit, your doctor will give you a physical exam (and evaluate any present symptoms) and take a medical history. You can also expect questions about your symptoms – when they began, how often they occur and the kinds of foods you associate with the reaction. This information will enable your doctor to decide which diagnostic tools to use to identify the allergen.
 
Depending on your symptoms – and the information you provide about your diet – your doctor might suggest starting with a food diary. This method involves keeping a record of what you eat and whether it triggers a reaction.
 
A typical next step is an elimination diet. With this, your doctor will advise you to eliminate the potential allergy-inducing food from your diet. Then, under your doctor's care, you reintroduce the food and see if your symptoms return. If they do, you might have a food allergy.
 
A number of faster and, at times, more precise tools can help doctors make a diagnosis. Depending on your symptoms, your doctor may, in fact, skip the first two steps (food diary and elimination diet) and start with one of the following: 
  • a RAST (radioallergosorbent) test, which is a blood test that looks for IgE antibodies. These antibodies indicate a faulty immune response to an allergen. Though used widely for their quick results, RAST tests come with a high false-positive rate and should be used in tandem with other diagnostic tools.
  • a scratch test (also called a prick test), during which your doctor will place possible food allergens on your back or forearm. Positive tests reveal swelling or red patches of skin. At times, these tests show a positive result for foods that have not triggered a reaction. This does not mean you have a food allergy. Doctors typically only diagnose an allergy when the scratch test matches your history of reactions.
  • an oral food challenge, which doctors view as one of the most accurate - though time-consuming and expensive - ways to diagnose an allergy. Carried out under close supervision, patients swallow capsules with potential food allergens and then wait a few hours to see if a reaction occurs.
If your symptoms are severe, your doctor will likely advise against a scratch test or an oral food challenge because of the health risk of exposing you to an allergen.
 
Diagnosing a food allergy, though lengthy and multi-stepped, can improve and possibly save your life. See your doctor if you suspect a food allergy, and start keeping records of what you eat and how you react to each food. For more severe reactions, seek help right away. With your doctor's support, you can come up with an avoidance plan to steer clear of the allergen – and to protect yourself if it crosses your path again.
 
Resources
 
Dugdale, D. (2008). Anaphylaxis. Retrieved March 15, 2009, from the Medline Plus Medical Encyclopedia Web site: http://www.nlm.nih.gov/medlineplus/ency/article/000844.htm.
 
Greene, A. (2002). Diagnosing food allergies. Retrieved March 15, 2009, from the Dr. Greene Web site: http://www.drgreene.org/body.cfm?id=21&action=detail&ref=1258.
 
Mayo Clinic. (2009). Food allergy. Retrieved March 15, 2009, from the Mayo Clinic Web site: http://www.mayoclinic.com/health/food-allergy/DS00082/DSECTION=causes.
 
Parker-Pope, T. (2009). Telling food allergies from false alarms. Retrieved March 15, 2009, from the New York Times Web site: http://www.nytimes.com/2009/02/03/health/03well.html?_r=1&pagewanted=print.