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Q. I’ve been tested twice for allergies; the last time was two years ago. My allergist wants to retest me. How often do I need to be retested for allergies?

A. Two years between allergy tests is reasonable – there are no limitations to the frequency of testing. But you can talk with your allergist about whether retesting is necessary.

Allergists will typically recommend retesting for symptomatic or therapeutic reasons.

Symptomatic

If you’re on an allergy medication and allergen avoidance plan for two years, and your symptoms recently returned or worsened, then these may be reasons to retest.

Perhaps you have symptoms in a new season that you didn’t have before? Your allergist may suspect there is a new allergy that wasn’t identified on the initial tests. Allergies are not static – studies show people can gain new allergies over time.

Allergy treatment should begin with an avoidance plan – and allergy testing will drive that plan. Just because we knew exactly what you were allergic to two years ago doesn’t mean we know everything you’re allergic to today.

Therapeutic

Based on how your medications are working or your history of symptoms, your allergist may recommend immunotherapy, or allergy shots that will help your body build tolerance to your allergens. This is typically a 3- to 5-year time commitment.

In that case, your allergist will want to retest you to confirm your allergens and that the immunotherapy plan is appropriate.

At my practice, a patient may come in with springtime allergies but testing reveals allergies to cats, house dust mites and mold. The patient feels symptoms all of the time, but especially during springtime. So feeling lousy becomes baseline.

Those are the people who need year-round treatment, even though they came in seeking care for seasonal symptoms. After treatment, many of these patients come back to me and say, ”You mean, this is how I’m supposed to feel all the time?”

Q. Can medications affect the validity of a skin prick/puncture test? Would being on certain medications affect how strongly a person reacts during a skin test?

A. Yes, several medications can affect skin testing responses. An allergist will always do a positive and a negative skin test control, which helps to determine if a medication that would interfere with the allergic response has inadvertently been taken.

Antihistamines are the drugs most commonly associated with suppression of the skin test response. Any medication that suppresses histamine will reduce or prevent the swelling and redness at the skin testing site. Swelling and redness at the skin test site indicate that a patient is allergic to the allergen being tested.

For best results from your skin test, you should avoid most antihistamines for at least 7 days prior to skin testing. Many guidelines only recommend 3-4 days of avoidance prior to skin testing, but a significant number of patients will still have some reduced skin test response for up to 7 days.

Exceptions to the 7-day rule include hydroxyzine (“Atarax”), which should be stopped 10 days prior to allergy testing, and diphenhydramine (“Benadryl”), which can be taken until 48 hours prior to allergy testing.

Patients who are taking psychiatric medications (such as amitriptyline, quetiapine, doxepin, and imipramine) can also have skin test suppression. However, no patient should stop these medications without discussing this decision with their psychiatrist or primary care physician. The allergist can help the patient decide if they need to stop the psychiatric medication, or if an alternative method of allergy testing should be considered.

Another group of medications, called beta-blockers, are often prescribed for high blood pressure. While these medications will not interfere with the skin test response, they can introduce more risks for allergy testing in the case of a serious reaction. Beta-blockers can slow the patient’s response to epinephrine, which is used for treatment in event of an allergic emergency. This is a very rare event, but most allergists prefer for patients to be off beta-blockers for allergy testing. This decision should be made with an individual patient, and only after the allergist discusses the matter with the patient’s cardiologist or primary care physician to determine which course of action holds the least risk for the patient. As with antihistamines, ideally the beta-blockers should be stopped at least 5-7 days prior to allergy testing.

Q. If you are getting either the scratch test or the injection test done, is it common practice for everyone to leave you alone in the room?

A. The protocol for staff activities after the placement of skin tests varies across different practices. Some practices may leave the patient alone in the room; some may have a staff member sit with the patient the entire time; other practices may have the patient return to the waiting room. There is no standard or common protocol for this portion of the testing procedure.

Q. A family member had a blood test called IgG to check for any delayed allergies. It showed milk and eggs to be a severe, but delayed allergy (no skin reaction). Is there a blood test that can check if she has a delayed allergy to other birds’ eggs (i.e. turkey, duck, quail, etc.) and other animals’ milk (i.e. goat milk, sheep milk, or maybe unpasteurized raw cow milk, etc.)?

A. In IgG testing, the blood is tested for IgG antibodies instead of being tested for IgE antibodies (the antibodies associated with food allergies). IgG is a “memory antibody”. 

When you have a blood test to query response to an immunization, this is also IgG testing. A common example is a “Rubella titer.” 

In the context of food, IgG signifies memory through exposure to a food.  Because a normal immune system should make IgG antibodies to foreign proteins (to include foods), a positive IgG test to a food is a sign of a normal immune system, and suggests tolerance or “memory” of the food rather than food allergy.  Therefore, IgG testing is not recommended for evaluation of food allergies.

If the patient has previously eaten the food (milks, eggs), he or she would likely have IgG to the food.