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Why Your Doctor May Recommend a Blood Test To Diagnose Your Allergies

Has your allergic rhinitis gotten the best of you?

If you’re like millions of Canadians, you suffer from some form of allergies. Whether it’s seasonal hay fever or an indoor dust allergy, the symptoms that come with this condition are enough to make daily life quite challenging.

To pursue any kind of effective treatment, you’ll need to pinpoint the exact cause of your symptoms. Knowing the culprit behind your coughing and sneezing is necessary if you choose to receive allergy shots or if you just want to take steps to eliminate the allergen from your home.

Most doctors will recommend a skin test to diagnose your allergies. But they aren’t recommended for everyone. For some patients, a blood test is the preferred method to identify the allergen causing your condition.

When Blood Testing May be Recommended

Because skin tests involve small injections of multiple allergens, some patients may react badly to the procedure. In rare cases they can cause severe allergic reactions that could be dangerous for certain individuals. If you have any of the following conditions you should talk to your doctor to discuss appropriate options for testing to diagnose your allergies:

  • A Heart Condition. If you have an unstable heart, skin tests will not be recommended for you. The potential side effect of a severe allergic reaction puts you at risk for a heart attack.

  • Severe Asthma. If you have trouble controlling your asthma symptoms, a skin test may also be too risky.

  • Taking Certain Medications. Doctors don’t recommend skin tests for those patients on anti-depressants, antihistamines, or steroids. These medications can interfere with the test and give faulty results.

  • Severe Skin Conditions. Skin tests could also cause problems for those patients with eczema, dermatitis, psoriasis or any other kind of severe skin condition.

  • A History of Anaphylaxis. Anaphylaxis is an extreme allergic reaction that can be life threatening. Patients who have a history anaphylaxis will be advised to use blood testing.

  • Intolerance to Needles. Skin testing involves many small injections. If you have a strong aversion to needles, skin tests will not be the preferred option.

If any of the above conditions applies to you, your doctor will likely order a blood test rather than a skin test to identify the allergen causing your symptoms. Your allergist may also recommend a blood test to determine if your allergy shot treatment is effective and producing the desired results. Doctors also use blood tests to check and see if a patient has outgrown an allergy.

Blood Tests: What’s Involved

To perform a blood test, your doctor will take a sample of your blood and later send it to a lab for analysis. Once there, the technicians will expose your blood to various allergens. Typically they will choose the ten most common allergens found in your area. They may also include specific food or other allergens your physician suspects you may be allergic to.

Technicians will then measure the amount of allergen-specific antibodies in your blood. When you have an allergy to a certain substance, your body creates specific antibodies to fight off that allergen once exposed to it. It’s these antibodies that reveal to the lab technicians the exact allergen your body reacts to.

The two most common types of allergy blood tests are:

  • Enzyme-linked immunosorbent assay (ELISA, or EIA)

  • Radioallergosorbent test (RAST)

Nowadays the most commonly recommended test is the ELISA test.

A positive test result means the lab found allergen specific antibodies in the blood sample. Do keep in mind that sometimes a patient can test positive for a certain allergen without ever having had a reaction to that substance.

The Advantages and Disadvantages of Blood Tests

Because your doctor only has to draw blood one time, rather than make the multiple injections required of skin tests, blood testing is a great option for those patients who have a low tolerance of needles. For infants and small children, blood testing is the preferred alternative for this reason. Doctors can also use blood tests on patients who take medication.

But blood tests do come with some disadvantages.

Because they are more expensive than skin tests, some health plans do not cover blood tests. They are also not as sensitive as skin tests, so you might not get the most accurate results. And finally, you may have to wait days or weeks before receiving your final results from the lab. When you get a skin test, the results are almost immediate. Your doctor can diagnose the allergen you react to during the actual test.

Educate yourself on the pros and cons of both skin and blood testing and talk to your doctor about which one is right for you. Once you diagnose your allergy, you can then find the best allergy treatment and be well on your way to finding relief for your symptoms.

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