Category Archives: Allergy Tests

Inappropriate test for food allergy – ALCAT

ALCAT_Logo

ALCAT is a test marketed to test for food allergy or food intolerance. It basically measures changes in the white-cell diameter after laboratory challenge to numerous different allergens or substances. Unfortunately, this method has not been scientifically validated and has no concrete published evidence. When blinded samples were sent, the test demonstrated no reproducibility (This means when the same sample were sent twice, the results came out completely different even though they were from the same sample).

The test also could not demonstrate food allergy or intolerance in patients that had true diagnosis of food allergy or intolerance. It is important to get proper evaluation by a trained and certified Allergist for evaluation of your food allergy.

Below is the statement position by the Australasian Society of Clinical Immunology and Allergy:

Cytotoxic testing (also known as Bryans’ or ALCAT testing)

Use: Diagnosis of food sensitivity / allergy.

Method: A suspension of patient white cells is incubated with dried food extracts on a microscope slide. Changes in the appearance and movement of cells are interpreted as representing a sensitivity or “allergy” to that food. The ALCAT test is a variation, whereby a mixture of blood and food extracts is analysed in an automated Coulter counter.

Comment: These results have been shown to not be reproducible, give different results when duplicate samples are analysed blindly, don’t correlate with those from conventional testing, and “diagnose” food hypersensitivity in subjects with conditions where food allergy is not considered to play a pathogenic role.

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Skin prick test

One of the  many techniques a qualified Allergist use to diagnose allergy is the skin prick test. Properly performed, it is the most accurate method to diagnose allergic sensitization and better than any simply ordered blood test panel.

Skin prick test involves direct testing of the allergen on the person suspected of allergy (in-vivo) thus the results are individualized to the person being evaluated. As a result, skin prick testing is the gold standard in which other indirect testing are compared to.

The skin prick test is a painless procedure and results from the skin prick test can be interpreted within 15 minutes. As a result, the Allergist can have immediate interaction with the patient for proper clinical correlation.

When scheduled for a skin prick test, please avoid antihistamines as these medications can interfere with the result of the skin test.

Medications that can interfere with skin prick testing

No prescription or over the counter antihistamines should be used 5 to 7 days prior to scheduled skin testing.  These include cold tablets, sinus tablets, hay fever medications, or oral treatments for itchy skin. Some allergy eye medications have antihistaminic activity and will need to be discontinued prior to testing. Examples include but not limited to (Aerius, Atarax, Claritin, Clarinase, Panadol Cold Flu, Pataday, Polaraimine, Piriton, Promethazine, Telfast, Xyzal, Zyrtec)

Other prescribed drugs, such as amitriptyline hydrochloride (Elavil), doxepin (Sinequan), and imipramine (Tofranil) have extended antihistaminic activity and should be discontinued at least 2 weeks prior to receiving skin test.

Asthma inhalers (inhaled steroids and bronchodilators), leukotriene antagonists (e.g. Singulair, Accolate) and oral theophylline (Theo-Dur,T-Phyl, Uniphyl, Theo-24, etc.) DO NOT interfere with skin testing and should be used as prescribed.

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Do not use only blood tests to diagnose food allergy

The diagnosis of food allergy requires detailed history taking, followed by physical examination and appropriate testing to confirm the suspicion of food allergy. Patients with Atopic Dermatitis/Eczema produce very elevated levels of IgE and as a result, will produce a lot of “false positive” results in their blood tests. As a result, please see a qualified Allergy & Immunology specialist for proper evaluation and treatment.

Study warns of over-reliance on blood tests for food allergy

Last Updated: 2010-11-05 15:04:20 -0400 (Reuters Health)
By Megan Brooks
NEW YORK (Reuters Health) – In the absence of anaphylaxis, food-specific IgE tests aren’t sufficient evidence for cutting out food from a child’s diet, clinicians from Colorado warn in a report published online October 29 in The Journal of Pediatrics.
In a study of more than 100 children on food elimination diets based on positive serum IgE immunoassay results, oral food challenges (OFCs) demonstrated that most of the foods were being unnecessarily eliminated from the diet.
“The key message from our paper is that we need to be selective in ordering these serum blood tests for food allergy and be careful in interpreting the results before placing children on what may be unnecessary elimination diets, especially in children with atopic dermatitis,” first author Dr. David M. Fleischer from National Jewish Health in Denver, told Reuters Health in an e-mail.
“A referral to an allergist for possible supervised food challenges to truly determine whether or not there are food allergies may be necessary in some patients,” he added.
Dr. Fleischer’s team reviewed the charts of 125 children ages 1 to 19 years. Clinical history, prick skin test (PST), and serum allergen-specific IgE test results were obtained and all of the children underwent at least one OFC to determine IgE-mediated reactivity to a suspected food. The vast majority of the children (96%) had active atopic dermatitis at the time of evaluation.
The decision to perform OFCs was based on a combination of factors, the authors say, namely, a history of ever ingesting the food, the type of reaction, patient age, PST wheal size and food-specific immunoassay results.
OFCs were not performed on children with a history of a life-threatening reaction; a convincing history of a reaction within the previous 6 to 12 months; an immunoassay test result (level) that exceeded 95% predictive value for milk, egg, peanut, or fish; or an associated large PST.
According to the investigators, 89% of OFCs (325 of 364) performed with foods being actively avoided at baseline were negative. The foods included milk, egg, fruits, meats, shellfish, peanut, soy and wheat.
The authors point out that all reactions during the OFCs occurred within the two-hour observation period. There were no documented cases of atopic dermatitis flares on the day after an OFC.
“Depending on the reason for avoidance, 84% to 93% of the foods being avoided were returned to the diet after an OFC, indicating that the vast majority of foods that had been restricted could be tolerated at discharge,” Dr. Fleischer and colleagues report.
They further point out that many of the children were unnecessarily on “overly restrictive” diets that excluded foods that they had never eaten or foods that they once tolerated, based primarily on immunoassay test results.
“These tests are commercially available for any practitioner to order, but they should only be ordered if the clinical history is suggestive of a possible IgE-mediated reaction to a food,” Dr. Fleischer advises.
“The practice of ordering a large panel of serum IgE tests and eliminating a large number of foods without the expertise of a specialist such as an allergist to interpret these tests properly needs to change,” he added.
Compounding the problem, as the researchers note in their report, is that not enough allergy practices and centers perform OFCs, possibly due to cost or safety issues. In addition, managed care organizations may discourage referrals to specialists who can help interpret immunoassay test results.
“Unfortunately, we occasionally see children with failure to thrive due to severe dietary restriction based solely on in vitro immunoassay testing,” they note.

SOURCE:http://link.reuters.com/hur63q
J Pediatrics 2010.

 

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Do not simply evaluate food allergy with blood screening panels

When evaluating food allergy, it is very important to seek appropriate consultation with a trained and board certified Allergy and Immunology specialist. The first approach towards evaluating food allergy is to conduct a thorough medical history to determine: if food allergy is likely and what the most likely culprit food is.

A limitation in blood panel testings is the false positive results because of non specific antibody binding in the laboratory test. As a result, a patient might be told to avoid certain foods that he/she has been consuming without any problems. It is very important to understand that a positive IgE test towards a particular food does not necessarily diagnose food allergy towards the food. On the other hand, a person might be allergic towards a particular food and have negative blood test. As a result, it is not recommended that patients pursue broad screening panels to screen for food allergy without proper supervision by an Allergy & Immunology specialist.

There are instances when blood tests are appropriate. When a food allergy is appropriately diagnosed, blood tests can be done to monitor IgE levels of a specific food to determine if a person is “growing out” of the food allergy. Ultimately, an oral food challenge needs to be done to determine if the food allergy has been out grown.

Finally, there are tests being offered to diagnose food allergy by testing to IgG and IgG4. At present, these tests lack scientific evidence to support its use in the evaluation of food allergy.

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