Clinical continued...

Physical

• The physical examination findings are most useful for assessing overall nutritional status, growth parameters, and signs of other allergic disease, such as atopic dermatitis, allergic rhinitis, or asthma.
  
  
• Findings from a comprehensive physical examination can help rule out other conditions that may mimic food allergy.

Causes

• Any food protein can trigger an allergic response, and allergic reactions to a large number of foods have been documented; however, only a small group of foods account for most of these reactions.
  
  
• Eggs, milk, peanuts, soy, fish, shellfish, tree nuts, and wheat are the foods most often implicated in allergic reactions that have been confirmed in well-controlled blinded food challenges.
  
  
• Investigations of near-fatal or fatal anaphylactic reactions following food ingestion reveal that most are caused by peanuts, tree nuts, and shellfish.

Differentials

Anorexia Nervosa
Bulimia
Celiac Sprue
Clostridium Difficile Colitis
Constipation
Diverticulitis
Dumping Syndrome
Esophageal Motility Disorders
Esophageal Spasm
Esophageal Stricture
Esophagitis
Factitious Disorder
Food Poisoning
Gastritis, Acute
Gastritis, Chronic
Gastroenteritis, Bacterial
Gastroenteritis, Viral
Gastroesophageal Reflux Disease
Giardiasis
Hiatal Hernia
Inflammatory Bowel Disease
Intestinal Motility Disorders
Irritable Bowel Syndrome
Lactose Intolerance
Trichosporon Infections
Urethral Diverticula
Urticaria
VIPomas
Vocal Cord Dysfunction
Wasp Stings
Whipple Disease

Workup

Lab Studies

• Serum testing for specific IgE antibodies to foods
  
  
  • Specific IgE antibodies to foods can be measured by in vitro laboratory methods (eg, IgE radioallergosorbent testing), which offers advantages when dermatographism, generalized dermatitis, or a clinical history of severe anaphylactic reactions to a given food limit skin testing.
    
    
  • This form of testing provides information similar to prick skin tests, but it is more expensive and generally less specific.
    
    
  • The CAP System fluorescent-enzyme immunoassay (FEIA) (Pharmacia Diagnostics, Uppsala, Sweden) provides a more quantitative method of determining allergen-specific IgE to food allergens.
    
    
  • When compared with the outcome of well-controlled oral food challenges, results of the CAP system FEIA are generally similar to those of prick skin tests in predicting symptomatic food allergy.
    
    
  • Quantitating food-specific IgE antibodies with this automated system can help identify patients who are highly likely to have allergic reactions (>95% probability).
    
    
  • Published positive and negative predictive values using this system are available. These predictive values aid in making the diagnosis, thereby reducing the need for confirmatory food challenges in some patients.
    
    
  • Currently, the predictive values of CAP System FEIA results are limited to several major food allergens (ie, egg, milk, peanut, fish).
    
    

  • The predictive values developed using the CAP System FEIA are useful in predicting the likelihood of a reaction but do not predict the severity of a reaction  

• Peripheral serum measurements of eosinophils or total IgE concentrations: Results from these tests support but do not confirm the diagnosis of food allergy. Likewise, normal values do not exclude diagnosis.

• Basophil histamine-release assays: These tests are mainly limited to research settings and have not been shown conclusively to provide reproducible results useful for diagnostic testing in a clinical setting.