Tag Archives: Blood test

Oral food challenge to peanut

Food allergy is a very common and even popular disease to have.  This results in some predictable patient behavior such as:

1.       I have allergy based on a blood test only, and I tolerate this food all the time.  This may not be allergy at all, but simply a condition called “asymptomatic hypersensitivity”.  Relax, some foods you can eat without allergy symptoms even though a blood or skin test is positive. 

2.       It is fashionable nowadays to have gluten sensitivity.  Many patients will perform gluten challenges at home to see if bread or starches make abdominal cramping, skin rashes, or even concentration problems improve or worsen with the offending food.  This practice becomes a problem if you are concerned with anaphylaxis (difficulty breathing, low blood pressure) to foods such as peanut, milk, or eggs to name a few.  It’s one thing to experience more abdominal bloating after a gluten challenge and a much more dangerous situation to lose consciousness after ingesting peanut. 

3.       I’m grateful to be a member of the American Academy of Allergy, Asthma, and Immunology (AAAAI) in part because they help me as an allergist to stay current of all the thousands of recommendations published every year on my specialty.   One such service is “Ask the Expert” forum and I’d like to share a recent post with you about food challenges.

Here’s the take-home message and the full answer is available if you click on the link below:

1.       Food anaphylaxis can be related to the total amount of food ingested.  In other words, don’t assume that tolerating a very small amount of peanut will guarantee that you can tolerate peanuts ad lib!  Food challenges are performed under close supervision in order to determine HOW sensitive you are. 

2.       Oral desensitization to foods is still in the research stage and the experts on treating food allergy do not recommend this procedure be performed outside of a research protocol.  It only takes one bad outcome to taint any progress made with treatment of food anaphylaxis.

Anyway, it’s lunchtime, and talking about food does make me hungry!

Oral food challenge to peanut.

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Pollens are bad out there, but when to test?

Allergy tests should be used only to confirm a diagnosis that has already been made on the basis of symptoms and medical history, advise 2 leading allergists in an article published in the January issue of Pediatrics.

Scott Sicherer, MD, from Mount Sinai Hospital in New York City, and Robert Wood, MD, from the Johns Hopkins Children’s Center in Baltimore, Maryland, reviewed the benefits and limitations of blood tests and skin-prick tests in the detection of allergic diseases.

Both the skin-prick test (SPT) and sigE test detect a sensitized state. “However, detection of sensitization to an allergen is not equivalent to a clinical diagnosis. In fact, many children with positive tests have no clinical illness when exposed to the allergen,” Dr. Sicherer and Dr. Wood write.

They further point out that testing for allergens that do not make sense (because they would never be encountered in the patient’s environment or because the patient is obviously not allergic to them) could lead to “detrimental actions of unnecessary allergen avoidance.” They also warn against a false-negative on an SPT or sigE test when a child is obviously allergic to a particular trigger.

The allergists identify circumstances in which SPT and sigE are warranted:

  • To confirm a suspected allergic trigger after observing a child react
  • To monitor the course of a food allergy to detect when it might be waning or outgrown
  • To confirm allergy to an insect after an anaphylactic response, and to identify allergies to vaccines (SPT only).

SPT and sigE tests should not be used, Dr. Sicherer and Dr. Wood write, to screen for allergies in nonsymptomatic children or to diagnose food allergies or drug allergies. Food allergies should be assessed with food challenges, they write, and skin and blood tests do not detect antibodies to drugs.

The tests might be useful for identifying the trigger of a respiratory allergy (allergic asthma or seasonal or perennial allergic rhinitis) that is ubiquitous but not obvious in the patient’s environment: for example, SPT or sigE can detect allergy to dust mites, animal dander, cockroaches, molds, or pollen.

Pediatrics. 2012;129:193-97.

The Teen Who Can’t Swallow–What To Do?

The Evaluation of a Patient With Suspected EoE

Our series is on eosinophilic esophagitis (EoE) and I’ve covered how you present with this condition and a little bit about what the heck this condition really is! The website reference is http://www.medscape.com/viewarticle/754206?src=mp&spon=38

Patients with suspected EoE should be evaluated by both an allergist and a gastroenterologist.

  • A careful history should include screening for the presence of reflux/GERD, growth delay, feeding/swallowing difficulty, and a past history of allergic disease. 
  • Symptoms of interest include history of weight loss or poor weight gain, dysphagia or odynophagia, multiple emergency department visits for impacted food, altered eating habits such as food aversions, overcutting or overchewing one’s food or eating very deliberately and requiring lots of fluids to wash down each bite.
  • A family history of similar symptoms or atopy can also be a clue.
  • EGD with multilevel biopsy is needed to make the tissue based diagnosis. Careful attention should be paid to gross features when performing the procedure. Dilation may frequently be performed in conjunction with the biopsy.

Allergen testing should be performed only in patients with biopsy proven EoE, because the tests do not have good positive predictive value without established disease.  Unfortunately, skin testing can be positive AND negative in biopsy proven EoE, which leads to much confusion from a diagnostic standpoint. 

Testing is guided by foods reported to cause symptoms, but should include 13 common foods with established predictive values for EoE.   What are those foods? I’m glad you asked.  Milk, egg, soy, wheat, corn, beef, chicken, apple, rice, potato, peanut, oat, barley. This means BOTH skin testing and patch tests to the above list.  Patch testing is a bit different in that I make a “paste” with the food and place it in a Finn chamber on the back for 48 hours.  Keeping it on can be a challenge, but good results.   

Patch test applied to skin
Loading a Finn chamber for patch testing

Inhalants should also be tested given aeroallergy can play a role.  Food atopy patch testing assesses for a cellular-mediated mechanism, and should be placed for food items not positive on initial testing, and read at a minimum of 48 hours after placement. Both prick and patch tests have independent positive and negative predictive values, as well as combined values. Foods positive on either test are generally recommended to be removed from the diet. There is no established role for ImmunoCAP® testing or other allergy blood tests in diagnosing EoE. 

  • So there you have it…find out if EoE is even present before testing for foods.
  • Use both skin tests and patch testing to identify suspected foods that will need to be eliminated.
  • And in case you’re wondering, here’s what a positive patch test looks like…..

    Positive patch test for EoE.