July 18, 2022

Allergy Blood Tests - What It Is & What You Need to Know

Key Takeaways

  • Allergies arise when your immune system reacts to a foreign substance and produces antibodies to counteract its presence.
  • Allergies cause a wide range of symptoms; from mild symptoms like a runny nose to life-threatening reactions like anaphylactic shock. 
  • An allergy blood test measures the amount of immunoglobulin E (IgE) in your blood. 
  • An allergen-specific IgE test can show you that you have an allergy to the specific allergen that was being tested for. However, it can not show you how serious your allergy is.

What comes first, the first day of spring or the arrival of allergy season? For many people, blooming flowers and temperate weather doesn’t signal a farewell to cold - it’s the arrival of constant coughing, sneezing, and watery eyes. 

But what are you allergic to? Is it the grass? Pollen? The dog next door? Or something else? A good way to find out if you have an allergy is to take an allergy blood test to measure your IgE antibodies. In this article, we will review allergy blood tests, how to get one and how to understand the results. 

What Are Allergies? 

Allergies can come in many forms, from those that cause a life-threatening reaction to medications, such as penicillin, to those that cause a reaction to a particular food, such as nuts and shellfish or by animal dander and mites. Some people are allergic to insect stings, while others suffer from allergic rhinitis caused by plant pollens.

If you are living with an allergy, you know how difficult it can make life, particularly if the allergen is something that you may often come into contact with. 

Allergies arise when your immune system reacts to a foreign substance. Your body identifies the allergen as harmful, even though it is not, and produces antibodies to counteract its presence. Consequently, each time you come into contact with the allergen, your immune system can cause one or more of the following allergy symptoms:

  • Hives or other skin condition, like dermatitis or eczema
  • Runny or stuffy nose
  • Sneezing
  • Headache
  • Cough
  • Sore throat
  • Swollen lips, face, or tongue
  • Difficulty breathing
  • Sore, watery eyes

The severity of an allergy varies from individual to individual. In some cases, allergies can be life-threatening if not treated quickly, leading to anaphylactic shock. Anaphylaxis can be fatal. Although in many cases, allergies cannot be cured, they can be treated with medications.

What Is an Allergy Blood Test?

A radioallergosorbent test (RAST) is a type of allergy test. It measures the amount of immunoglobulin E (IgE) in your blood. This substance is an antibody that is made by your body in response to an allergen. If you have an allergic reaction, you will have more IgE in your blood than you normally would. There are two types of IgE tests:

  • Total IgE Test: This test is performed to measure the total amount of IgE in your bloodstream. 
  • Specific IgE Test: This test is performed to measure the amount of IgE your body produces in response to a specific allergen. You will need a separate test for each allergen. 

When Should I Get an Allergy Blood Test?

You should get an allergy blood test if you are experiencing any of the symptoms listed above or if you have persistent lung, skin, or digestive problems, or if a skin test isn’t possible. 

How Do I Get an Allergy Blood Test?

IgE tests are powerful tools for identifying allergies. You can have an allergy blood test taken at your healthcare professional’s office or you can opt for home testing with a mobile lab service, such as Getlabs. In this case, a Getlabs specialist will come to your house, take a sample of your blood, and take it to a laboratory for analysis. All you have to do is wait for your results. 

What Should I Do Before My Allergy Blood Test?

Usually, you don’t need to make any special preparations before your allergy blood test. In some cases, particularly if you are having blood drawn for other types of lab tests, your doctor may want you to fast before the test. This means avoiding food and drinking only water. If you are currently taking antihistamines, your doctor may ask you to stop taking them before the test. 

What Happens During My Allergy Blood Test?

Before taking your blood sample, your Getlabs phlebotomist will make sure you are sitting or lying in a comfortable position. Follow their instructions and use these tips to ensure you have a pleasant experience:

  • Explain fully: Tell the phlebotomist anything important about your medical history. For example, if you are taking any medications, have had any recent illness, or have had an unusual reaction to a blood test in the past (such as fainting, severe bruising, or swelling).
  • What to expect: The Getlabs phlebotomist will tie a tourniquet around your upper arm to make it easier for them to locate a suitable vein. They will insert a fine needle into the vein and attach a small container to collect your blood. When the sample has been collected, your phlebotomist will remove the needle and apply pressure to the needle site for a few seconds. They will then cover it will a small dressing. 
  • Remain calm: Stay calm during your blood test by taking deep breaths, listening to relaxing music, and looking away while the specialist inserts the needle into your vein. 
  • Take it easy: After the test, your specialist will apply a dressing to the needle site. You should leave this on for at least fifteen minutes. Avoid strenuous activity or heavy lifting for two hours after the test and do not put any pressure on your arm. 
  • Warning signs: If you have any feelings of dizziness, faintness, or signs of swelling and infection at the needle site, call your doctor immediately. 

When Can I Expect My Allergy Blood Test Results?

You can expect to receive your blood test results within 2-3 days. You will get a call from the lab or your doctor. You may need to make a follow-up appointment to discuss immunotherapy treatment plan for your allergy. If you have positive results, you may also need to see an allergist for an allergy skin prick test or a skin patch test.

How Do I Interpret My Allergy Blood Test Results

Allergy blood test results are based on a scoring system, which can vary slightly from lab to lab. Generally, the higher the number, the more likely it is that you have an allergy. 

Total IgE Test Results

The total IgE test measures the overall quantity of immunoglobulin E in your blood. Though it can indicate if you have an allergy, it cannot tell you what the allergen is. Nor can it tell you how serious your allergy may be. However, if the score on your test is low, it is unlikely that you have an allergy. Score values for a food allergy test are as follows:

  • 0.35 or lower:  unlikely allergy
  • 0.35-0.69: doubtful allergy
  • 0.70-3.49: possible allergy
  • 3.50-17.49: a greater possibility
  • 17.50-49.99:  allergy very likely
  • 50.00-100.00: very high likelihood
  • 100.00 or more: allergy extremely likely

Specific IgE Test Results

An allergen-specific IgE test can show you that you have an allergy to the specific allergen that was being tested for. However, it can not show you how serious your allergy is. If you have a low score on your specific IgE test, it is unlikely that you have an allergy.

Can My Allergy Test Be a False Positive?

Around 50% to 60% of allergy blood tests give a false-positive reading. This means that your test may show that you have an allergy when you do not have one. This can sometimes happen because your body is having a slight reaction to something in food you recently ate.

Have Blood Tests Done at Home with Getlabs

If your healthcare provider has recommended you take an allergy test, Getlabs can help you make it happen in the comfort of your home. 

You can easily book an appointment online and we will send a local phlebotomist to visit your home and collect your sample. They will then take your sample to a nearby lab for analysis. All you need to do is relax and wait for your results. Getlabs are dedicated to providing reliable diagnostic tests in person.

This page is provided for educational and informational purposes only and does not constitute the provision of medical advice or professional services. The information provided should not be used for diagnosing or treating a health problem or disease, and those seeking personal medical advice regarding any of the tests and conditions referenced above are advised to consult with a licensed clinician. Always seek the advice of your qualified health provider regarding a medical condition and do not disregard professional medical advice or delay in seeking it because of any information on this page. If you think you may have a medical emergency, immediately call 911 or go to the nearest urgent care center or hospital.

Book an at-home lab collection

Getlabs sends a nearby medical specialist to you to collect your labs for Labcorp and Quest. Available same-day, nationwide.

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