Who Should Get Allergy Shots?
From the time he was 12 months old, Paul was miserable in the spring and, to a lesser degree in the fall, with a runny nose, watery eyes, and itchy skin. By his third birthday, the pollen allergies also triggered asthma attacks. Prescription medications didn't help much to relieve his symptoms, even with constant use.
All this made Paul a good candidate for injections.
"Shots work extremely well in patients that clearly have allergic symptoms, either allergy in their nose like allergic rhinitis or bronchial asthma, where outdoor allergens like tree, weed and grass pollens seem to be a major cause," says Stanley P. Galant, M.D., an allergist in Orange County, Calif., and a clinical professor and director of pediatric allergy at the University of California, Irvine.
Patients with allergies to molds, house dust mites (microscopic insects that feed on human skin cells found on furniture, bedding and carpets), and animal dander (tiny skin flakes animals continually shed) don't respond quite as well to shots as those allergic to outdoor allergens, he says. But standardization of extracts for cat dander and dust mites and overall better preparations have increased effectiveness even for these patients, he adds.
Immunotherapy doesn't begin until after skin tests or blood tests have determined the exact culprits.
"You have to show that [the patients] have IgE antibodies to the allergens in question," says John Yunginger, M.D., a member of FDA's Allergenic Products Advisory Committee and a pediatric allergist at the Mayo Clinic, Rochester, Minn.
The first time an allergic person is exposed to an allergen, the immune system produces a kind of antibody called immunoglobulin E--IgE for short. (But it is rare for a first exposure to cause allergic symptoms. Only on subsequent exposures do typical allergic symptoms, such as sneezing, coughing and rash, appear.) Overproduction of IgE is characteristic of allergy reactions.
Deciding which allergens to test "depends very much on the patient's history," says Yunginger. "In somebody who has fairly straightforward classical seasonal symptoms they may get as few as 15 or 20 [skin] tests. Someone with more extensive perennial disease may get 75 or 80."
Each individual skin test consists of a small amount of the suspect allergen scratched onto the skin, usually on the back. If a hive with surrounding redness appears within 15 minutes, allergy to the substance is probable. The doctor also takes into account the dose of allergen and the size of the response.
Two controls, standards against which experimental observations may be evaluated, are also used to make sure skin-test reactions are caused by the allergens. One of the controls, which should not cause a reaction (no hive), is simply the diluting solution. The other control contains histamine, a naturally occurring substance that causes a hive in almost everyone.
According to Galant, the patient's history is as significant as the testing. "The history is really what tells me whether to put the patient on shots," he says. "Training as a specialist helps me interpret the data from the history and correlate that with the testing and come up with a solution."
While skin tests give quick results and can be done in the doctor's office, there are some cases where a blood test is preferable, says Marshall Plaut, M.D., chief of the allergic mechanisms section in the National Institute of Allergy and Infectious Diseases, National Institutes of Health. Individuals with skin problems or skin diseases are not good candidates for skin tests, he says.
Isadora B. Stehlin is a member of FDA's public affairs staff.