CPR First Aid

Allergy Blood Tests and What to Expect

Allergy Blood Tests and What to Expect

If you have been experiencing unexplained symptoms such as a runny nose, sneezing, coughing, or itchy eyes, you may have an allergy. Allergy blood tests are one way to determine the specific allergens that are causing your symptoms. The results of the test can help you and your doctor create a plan to treat your allergies. This post will discuss what to expect during and after an allergy blood test.

What are Allergies?

An allergy is a hypersensitivity reaction of the immune system to a particular substance, known as an allergen. Common substances that can cause allergies include:

  • pollen
  • dust mites
  • mould
  • pet dander
  • food
  • insect stings

People who suffer from allergies often experience symptoms such as sneezing, runny nose, watery eyes and itching. In severe cases, anaphylaxis is a potentially life-threatening reaction that can occur in Cheltenham or anywhere in the country.

There are several types of allergies, including seasonal allergies e.g. hay fever, food allergies, drug allergies and environmental allergies. Allergies can be treated with medication, but avoidance of the allergen is often the best way to prevent symptoms.

4 Main Types of Hypersensitivity

Hypersensitivity refers to an exaggerated response by the immune system to a particular substance. It is also known as an allergy. There are four main types: Type I, Type II, Type III and Type IV.

Type I Hypersensitivity

Also known as anaphylaxis or immediate hypersensitivity, it is a rapid and severe allergic reaction. It occurs when the body reacts to a foreign substance, such as pollen, bee venom or certain food, by producing antibodies called immunoglobulin E (IgE). These antibodies attach to cells in the body and release chemicals, histamine for one, that causes symptom such as wheezing, shortness of breath, coughing, swelling of the throat and a drop in blood pressure. Anaphylaxis can be life-threatening and requires immediate medical attention.

Type II Hypersensitivity 

An immune reaction occurs when antibodies bind to molecules on the surface of cells, causing them to be destroyed. This type of hypersensitivity can be triggered by drugs, such as penicillin, or by blood transfusions.

Type III Hypersensitivity 

A delayed allergic reaction occurs when immune complexes (antibodies and antigens) build up in the body and deposit in various tissues. This can lead to inflammation and tissue damage. Type III reactions are often seen in autoimmune diseases, such as systemic lupus erythematosus and rheumatoid arthritis.

Type IV Hypersensitivity 

Also known as delayed hypersensitivity, is a cell-mediated immune reaction that occurs when T cells (a type of white blood cell) recognize a foreign substance and release chemicals that cause inflammation. This type of hypersensitivity usually takes several days to develop and can be triggered by drugs, infections and certain chemicals.

Emergency Response to Hypersensitivity Reactions

Allergies can happen to anyone, especially if there is one member of the family who has an existing allergy. Severe cases of allergic reaction at home or in the workplace would require a trained person knowledgeable with skills to manage critical conditions or prevent further harm to the patient. CPR First Aid at Cheltenham teaches first aid practices that can be lifesaving. Contact us for first aid and CPR courses locally and anywhere in Australia.

Can Allergies be Detected in Blood Tests?

Allergies are caused by an overreaction of the immune system to a particular substance, and this overreaction can be detected in blood tests. However, keep in mind that not all allergies can be determined through blood tests such as food allergies.

Difference Between an Allergy Blood Test and Skin Test

An allergy skin test is when a small amount of allergen is placed on the skin, usually on the arm or back. If you’re allergic to the allergen, you’ll develop a raised, itchy bump or wheal.

On the other hand, an allergy blood test is when a sample of your blood is taken and tested for the presence of antibodies to a particular allergen. If you have these antibodies in your blood, it likely means you’re allergic to the allergen. Allergy blood tests are also used to measure the level of these antibodies. This can be helpful in determining how severe your allergy is. We’ll be talking more in detail about Type 1 hypersensitivity and allergy blood tests.

Types of Allergy Blood Tests

There are 2 general types of allergy blood tests to measure and identify IgE response.

Total IgE Test

Measures the level of immunoglobulin E (IgE) in your blood.

Specific IgE Tests 

Used to help diagnose allergies to things like pollen, dust mites, pet dander, and certain foods. The test can also be used to help monitor your body’s response to allergy shots (immunotherapy).

Why Take an Allergy Blood Test?

If you have allergy symptoms but aren’t sure what’s causing them, your doctor may recommend an allergy blood test. This test can measure your immune system’s response to different substances and help pinpoint the allergies you have.

An allergy blood test is also known as a radioallergosorbent test (RAST). This test works by taking a small sample of your blood and adding it to different substances that may be causing your allergies. If you’re allergic to one of the substances, your immune system will release antibodies in response. The test can measure the number of antibodies in your blood and give your doctor an idea of how severe your allergy is.

Conditions that may require an allergy blood test include:

  • hay fever
  • asthma
  • food allergies
  • hives
  • eczema

Your doctor may also recommend an allergy blood test if you have a family history of allergies or if skin prick testing doesn’t give clear results.

Advantages of RAST

If you or a loved one suffer from an allergy, testing is the best way to identify what you are allergic to and get relief. In summary, here are the pros of an allergic blood test:

  1. Highly accurate in identifying allergies.
  2. Can be used to identify allergies to substances that may not cause an obvious reaction, such as pollen or pet dander.
  3. Can be used to determine the severity of an allergy and whether it is likely to cause a severe reaction.
  4. Can be used to monitor the response to allergy treatment.
  5. Relatively quick and easy to administer.

What are the Disadvantages of Allergy Blood Tests?

There are a few potential disadvantages to allergy blood tests.

  1. They can be expensive. Insurance may or may not cover the cost of the test, so it’s important to check with your provider beforehand.
  2. Additionally, blood tests require a trained professional to administer them, which can add to the overall cost. 
  3. Usually, take longer to get results back than skin prick tests, you may have to wait a bit longer to find out what your allergies are.

How to Prepare for the Test?

Here are a few things you can do and remember prior to the blood test are:

  • First, it is important to avoid taking any antihistamines for at least three days before the test. This will ensure that your body will produce enough histamine for the test.
  • Second, you should make sure to drink plenty of fluids so that your blood will be easy to draw.
  • Finally, you should avoid eating anything for at least two hours before the test.

What to Do if You Get a False Positive Result?

A false positive allergy blood test is one where the test results show that you are allergic to a substance when in reality you are not. This can happen due to a number of different reasons, such as cross-reactivity (when another substance triggers a reaction in the body that is similar to an allergic reaction) or lab error.

While false positives are not common, they can occur, and it is important to be aware of the possibility. If you have a positive allergy blood test but do not have any symptoms of an allergy, your doctor will likely order additional testing to confirm the results.


There is currently no cure for allergies, but there are treatments that can help manage the symptoms. Allergy blood tests can be used to diagnose allergies and determine which substances a person is allergic to. These tests are generally safe and accurate.

As a Cheltenham first aider, you will be able to advise the patient on the things to prepare when a coworker or a family member decides to take an allergy blood test. If you’d like to know more about our first aid courses at Cheltenham, we’ll be happy to answer your queries at CPR First Aid.

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