Allergy Testing

Q. Is it true that a simple blood test can help you find out if you have allergies?

A. Actually, the first step in diagnosing allergies is a thorough health history and physical examination. Allergy tests, such as skin tests or blood tests, confirm what your health history tells the allergist. If your doctor were to rely exclusively on the results of the allergy test without history and physical examination, you could be diagnosed as having an allergic problem you may not have.

Allergists prefer using skin tests because:

• The results are available immediately.
• The testing is less expensive.
• The tests are more sensitive to subtle allergies.

Sometimes a blood test is appropriate, particularly when:

• You can't stop taking medication before having skin tests.
• You have a skin disease like eczema or psoriasis.
• You are so sensitive to an allergen that even a slight exposure could be risky.

Your allergist will decide what tests to conduct based on your individual symptoms and needs.

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 prick 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.

Q. If a person has a runny nose, bleary eyes and is sneezing during pollen season, how important is it to see an allergist? Does it matter what you're allergic to, specifically? And are allergy shots – immunotherapy – worth the time and trouble?

A. It's definitely helpful to understand what triggers your symptoms, especially if you're having difficulty controlling them with over-the-counter medications, having complications like sinus infections or asthma, or feeling so run down that it affects your ability to work or go to school.

Symptoms can be hard to interpret, but a board-certified allergist has particular training and experience that help find answers. A patient with allergic sensitivity to pollen, for example, might not have symptoms after a minor exposure. But with heavy exposure, or with other allergens added in (like pet dander or dust mites), the patient's allergy threshold may be exceeded and they begin experiencing symptoms. That's why some patients have symptoms mainly during pollen season, but they're not just allergic to pollen. They may also have allergies to things like pets and dust mites, and if those other allergens were reduced, the individuals might be able to tolerate the higher pollen exposure.

Regarding allergy shots, how helpful they might be depends on the severity of the patient's symptoms. Allergy shots are most effective for inhaled allergens such as pollen and other environmental allergens, animal dander, and mold spores. The shots help build tolerance to an allergen so that the patient can tolerate exposure. This tolerance continues even after the immunotherapy ends, and most patients don't need allergy shots again.

Q. My allergist has performed skin tests, which have been of some help in diagnosing my allergies, but I'm curious about other options. What kinds of blood tests are available to check for possible food allergies?

A. There are two kinds of food allergy blood tests.

One is IgE-based and reflects the most common allergic reactions. You can work with your allergist to choose each food to be tested: shrimp, salmon, orange, peanut, etc.

Another type of food test measures IgG antibodies to foods. This test is controversial and has unclear clinical significance, since people can test positive without experiencing any clinical problems.

Your allergist can help you decide which tests will be most useful for your diagnosis.

Q. My son was diagnosed with peanut allergy by a screening blood test when he was 18 months old (done due to a family history of food allergy in first cousins), but he never had a major reaction to peanut before the diagnosis, and nothing has happened since. He is now 5 years old. He has had cookies that were made in a facility where peanuts are present, without any reaction. He recently had a negative skin test for peanut, and his last blood test level was 2.3. I was told that my son should continue to avoid peanuts. However, I recently read about a new kind of blood test for peanut allergy, and I am wondering if this test could be helpful for my son?

A. Peanut allergy seems to be on the rise in the US over the past decade. While there are some promising treatments being researched, the current standard of care is complete avoidance of peanut. Because this restriction can have such a major impact on everyone involved, it is very important that you receive an accurate diagnosis. Peanut allergy affects most areas of a person's life, from the home setting, to play dates, to school, to dining out and beyond.

The most important factor in making an accurate diagnosis of peanut allergy is the actual history reactions that have occurred upon consuming a peanut. One problem that allergists face, however, is that some people do not have a clear-cut history of reaction to peanut. In these cases, allergists will typically perform a skin prick test to gain more information. If the skin test is negative, an IgE blood test is the next step. If the blood test also comes back negative (meaning complete absence of peanut-specific IgE, or a very low positive result with no history of anaphylaxis or other serious reaction), an allergist will often proceed to an oral food challenge in the office to confirm the test results.

However, if the first blood test comes back positive, yet the clinical history is vague or indicates a mild reaction history, a new test, called the peanut "component test," may be used to help provide clearer information. This component test can determine which specific peanut proteins are triggering the positive test results. It is important to note that there are many smaller protein fragments that make up a whole peanut. Thus, when a person reacts to peanut, he or she may be responding to one or more different protein fragments in the peanut. Determining which of these protein pieces are causing the reaction is important, as some (scientific names Ara h 1 , Ara h 2 , and Ara h 3 ) carry more risk than others. Thus, if these specific tests are negative, there is less risk; if they are positive, there is a higher risk. 

These results can help guide your allergist in determing whether to perform an oral food challenge despite the positive initial peanut blood test. Given your son's unclear history of reaction to peanut, you should discuss the the peanut component test, and a possible oral food challenge depending on the results, with your allergist. No matter the results, these tests should provide you with useful information.

Q. I recently underwent a scratch test to determine what I'm allergic to. The results of all 45 allergens they tested were negative (with the exception of the histamine control), although I clearly have seasonal allergies. Is it so important that I learn the cause of the allergies, or should I just go ahead with the treatment that works (a combination of antihistamine and nose spray)? Are there panels of less common allergens available for scratch tests?

A. There are over 50,000 species of mold in air. You were undoubtedly not tested for all of those. The same is true for pollens and many other allergens.

Skin testing is typically done for the most common allergens. Many allergens, however, are less common or even unknown. If you tested negative to all 45 allergens, then you likely have either a sensitivity to a less common allergen or you have nonallergic rhinitis, which just seems like an allergy.

At any rate, you certainly can get on with treatment. A combination of nasal sprays, antihistamines and eye drops (if needed) should help. If not, there are other options that don't require knowledge of what specifically you are allergic to. Ask your allergist for advice.

Q. I have asthma and was sent to an ear, nose, and throat (ENT) surgeon (by my pulmonologist) because of a persistent sinus infection. Because of blocked passages, the ENT did surgery, which has helped some. He also did allergy testing to 19 allergens and told me I was highly sensitive to all of them. He wants me to start allergy shots (immunotherapy), but I question whether I may be allergic to additional, untested allergens. I don't want to go through years of time commitment and expense and still find myself miserable because of untested and untreated allergies. My question, then - would an allergist test for and treat more allergens than the ENT surgeon did?

A. These positive tests are only important if they match your personal allergy medical history. This correlation has far greater importance than the number of tests done, which can vary based on one's history, geographic location, etc. For example, a positive skin test to ragweed pollen is only meaningful if you experience allergic nasal and eye symptoms during the ragweed pollen season in the late summer. A positive test to dust mites is only important if you experience sneezing or itchy eyes when you vacuum or disturb indoor house dust. People without identifiable allergic triggers could have non-allergic nasal conditions.

If indeed you have symptoms that match your allergic sensitivities identified by skin testing, allergy injections may be useful in controlling chronic nasal symptoms and sometimes in preventing future sinus infections. Before going straight to allergy injections, however, we recommend that everyone have a good trial of medications known to be effective in controlling nasal allergy and preventing sinus infections - including nasal steroid sprays. Environmental control measures can also be helpful, depending on the allergen.

Most allergy sufferers feel board-certified allergists are more effective at relieving their symptoms. In a study, 54% of sufferers reported their allergist recommended a treatment plan that was more effective than any other non-allergist (such as ENT surgeon, family physician, etc.), or over-the-counter medication. An allergist is an expert trained at taking a detailed medical history, and interpreting allergy test results, and is successful in treating up to 90 percent of patients with seasonal allergies and 70 to 80 percent with perennial allergies.