A chat with the good doctor: how can the lab support the physician in the allergy march?

Medical Laboratory Observer, Sept, 2004 by Ed Susman

Primary-care physicians manage most allergy patients, but it is difficult for these clinicians to have comprehensive knowledge of the myriad laboratory tests available, which can ensure an appropriate diagnosis. Henry Homburger, MD, is a consultant in and professor of laboratory medicine at the Mayo School of Medicine and the Mayo Graduate School of Medicine in Rochester, MN. Homburger is also director of the Immunology Antibody Laboratory in the Department of Laboratory Medicine and Pathology at the Mayo Clinic. In a chat with the good doctor, Homburger discusses the clinician's dependence on laboratory expertise.

The primary-care physician sits on the front line of treatment and is expected to have expertise in areas of all kinds. Allergic reactions and allergy testing, however, can be an obscure area for many. If he suspects allergic disease in a patient, the doctor must have appropriate tests performed. Allergy testing can be very useful to primary-care physicians in particular. Depending on the test results, he then must decide whether to manage the patient or to refer the patient to a specialist.

With the profusion of available tests, the laboratory has to take a more assertive role in educating nonallergist specialists in appropriate test selection.

Forty years ago, the proliferation of the current plethora of allergy tests started. Laboratories reported the discovery of immunoglobin (IgE), shown to be responsible for the skin-sensitizing activity of serum from allergic-disease patients. On that discovery's heels came commercial tests that measure IgE protein and specific antibodies of the IgE class. Today, assays and reagents abound, and the technology and quality of today's tests are much improved. Better tests mean better treatment.

Laboratory technology has come a long way in developing reliable tests to quantify IgE levels. Early tests were relatively crude immunoradiometric assays that employed paper-disc immunosorbents made from allergen preparations of variable potency. Doctors had to wait for long incubations only to get results of negligible value that were often in disagreement from one laboratory to another.

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To date, improvements have produced quantitative assays that conform to industry standards. A database that correlates concentrations of different IgE antibodies to the likelihood of allergic disease is now also available.

Such knowledge of the practice environment enables laboratory scientists to provide clinicians with clinically useful reference ranges and thereby maximize the decision-making potential of the test results.

Age is the first consideration for the doctor who suspects patient allergy. Recent studies have shown that children who will develop allergic disease generally proceed through stages, with different diseases associated with sensitization to different allergens at different ages. In children, it is important to identify these sensitivities first so as to determine the antigens and minimize exposure to them.

* From infancy to 18 months of age, children who will be allergic tend to react to common foods such as milk, eggs, and grains.

* From age two to five years, children will still react to foods, but will also start becoming sensitized to dust mites, a common antigen that promotes asthma and respiratory disease in young as well as older children.

* After age five, children begin to react to certain types of inhalant allergens--molds and, to a certain extent, pollen--that may be present in the environment.

The laboratory must guide the appropriate use of tests by understanding what is known as the so-called allergy march--familiar territory for allergists, but perhaps not for primary-care physicians, pediatricians, general practitioners, or internists who are the most likely to initially see a patient with allergies.

Testing children two to three years old for pollen sensitivity without testing for food sensitivity is a mistake because of this sequence of sensitization, along with the sequence of clinical expression of disease that begins with eczema or atopic dermatitis in infants up to 18 months of age. That is followed by gastrointestinal symptoms and possibly some respiratory symptoms, including otitis and the beginning manifestations of asthma. Appropriate testing first determines whether a child is atopic and second, where he is on this continuum of disease and sensitization, both of which are determined via a relatively small number of IgE antibody tests at each age group.

Local hospital or reference labs can set up and conduct small panels of commercially available tests that will help primary-care physicians decide whether a child is likely to be allergic.

After determining the severity of clinical manifestation, the doctor may decide to refer the child to an allergist. The remaining question is to what extent antigen avoidance interrupts the sequence of sensitization and disease development in the allergy march. Right now, the evidence is equivocal. Some studies suggest minimizing antigen exposure allows decreased drug dosages and interrupts the sequence of sensitization that may prevent development of severe asthma. And that is the goal: to stop kids from getting asthma. Other evidence shows antigen avoidance is only partially effective in stopping the development of asthma. Enough evidence, however, indicates it does work and that symptoms can be reduced. Certainly, reducing the suffering and morbidity that accompany some of these disease would suggest it is simply good medicine to identify the sensitivities and administer the appropriate treatment.