How Accurate Are Skin and Blood Allergy Tests?

Allergies can have a detrimental effect on a person’s quality of life. Allergy symptoms can range from sneezing, congestion, watery eyes, itchiness, cough, post-nasal drip, rash, sinus pressure, asthma symptoms, or food reactions. Allergy testing can help determine if the cause is allergic in nature. An important question is whether skin or blood testing is more accurate for detecting an allergy. There is no clear answer to that question, and it depends on the patient, symptoms, medications, skin condition, risk factors, and what type of allergy is suspected.

Resource: medlineplus.gov

Estimated reading time: 6 minutes

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What Do Allergy Testing Methods Test For?

Generally speaking, most allergy blood tests and allergy skin tests test for the presence of an IgE-mediated allergy. IgE, or Immunoglobulin E, is an antibody that the immune system produces. Allergies happen when the patient’s immune system reacts to a substance that isn’t normally harmful.

Positive Allergy Test

This is an indication that the patient’s immune system has reacted to the allergen. This does not necessarily mean that the allergen is responsible for the patient’s symptoms. For some patients, they test positive for an allergen allergy test, but they rarely or never have symptoms associated with that allergen in the “real world.”

Negative Allergy Test

This is an indication that the patient does not have allergies to what was tested. However, this also may not rule out that the patient’s symptoms aren’t being caused by allergies. That is why it is important that a knowledgeable professional selects, performs, and interprets the allergy test.

How Does an Allergy Skin Test Work?

For an allergy skin test, the provider will use a minuscule amount of allergen on the skin or under the skin. Providers most often use a skin prick test. If the immune system reacts, a small bump usually appears at the test site. Providers call these bumps wheals. They may look like mosquito bites and may itch for several minutes.

Resource: my.clevelandclinic.org

How Does Allergy Blood Testing Work?

Allergy blood testing measures allergen-specific IgE antibodies in a blood sample. A provider draws a small blood sample, which is then sent to a lab for testing. The lab measures whether the immune system has produced IgE antibodies in response to specific allergens, such as pollen, dust mites, mold, pet dander, insect venom, or certain foods.

Blood testing does not require allergens to be placed on the skin, so it may be helpful for patients who cannot stop certain allergy medications, have widespread skin irritation, or have a higher risk of reacting during skin testing. Results are not available right away because the sample must be processed by a lab. Once results are ready, the provider will review them alongside the patient’s symptoms, medical history, and exposure history.

Resource: mayoclinic.org

Skin Test vs. Blood Test: Which Is More Accurate?

Providers often recommend skin tests first for many environmental allergies. Skin testing is fast, sensitive, and completed in the office. For some patients, blood testing may be a better choice since it doesn’t require exposing the skin and can be done even if the patient is unable to stop allergy medicines. Which test is right will depend on the question being answered.

Testing Considerations

• Results: Often available during the visit (skin) vs. generally available after lab processing (Blood)
• How it works: A provider applies the allergen to or under the skin.
• Medication considerations: Some allergy medicines may need to be stopped
• Skin-related issues: May be difficult to read with some skin conditions
• Typical uses: Seasonal and year-round allergies, most environmental triggers
• Major limitation: False positives or false negatives may occur

No one test is better than another for every patient. Both skin and blood tests can yield useful information. The most useful test for one patient might not be the right test for another, and results may be better interpreted in one patient than another.

When Skin Testing May Be Appropriate

Your provider may recommend skin allergy testing if your symptoms suggest you have seasonal allergies, year-round allergies, allergy-associated asthma, or allergies involving your sinuses. Skin testing may be the right choice when your provider wants fast in-office results, you can safely pause certain allergy medications, and your skin can be read clearly. Testing may help identify these common triggers:

• Trees
• Grasses
• Weeds
• Dust mites
• Molds
• Pet dander
• Certain foods, when symptoms suggest a food allergy
• Venom, in select cases

Your results may guide care, including allergen avoidance, medication, allergy shots, or allergy drops.

When Might Blood Testing Be Suggested?

A physician may suggest allergy blood testing when skin testing would be less helpful. This could be when patients are unable to discontinue taking antihistamines, have widespread eczema or other skin conditions, or have other medical factors that render skin testing more challenging.

Blood testing may also be used to acquire further information once skin testing has already been completed, or a physician would like laboratory-based IgE values for a particular allergen. Though a blood test is helpful, results must still be analyzed within the context of medical history and presenting symptoms.

Can Allergy Testing Ever Be Incorrect?

Skin and blood allergy testing can result in false positives and false negatives. A “false-positive” result implies a positive allergy to an allergen with which the tested person did not have any symptoms associated with the allergen. A “false negative” implies a negative result to an allergy test when the test person did have symptoms when coming into contact with the allergen. Medication use, skin condition, method of testing, allergens used, time of testing, and the type of allergy are all factors that can influence an allergy test result.

What Comes After an Allergy Test?

After testing is completed, the allergist will review results and indicate which of the allergens identified were most clinically relevant to the patient. Management options may include avoiding identified triggers, prescription or over-the-counter allergy medications, or immunotherapy. Your provider may recommend immunotherapy for some environmental allergies. Immunotherapy involves becoming desensitized to certain allergens over time via shots or drops, depending on patient and provider preferences.

Final Thoughts

The majority of allergy skin testing is the test of choice for many environmental allergies because of the immediate, sensitive results obtained in the physician’s office. An allergy blood test is a good alternative if skin testing is unsafe, not feasible, or not medically indicated. Contact Colorado ENT to schedule an appointment.