The Difference Between Blood Tests and Skin Tests for Allergies

Allergies occur when your immune system overreacts to a specific substance called an allergen, or trigger. Your immune system may identify the trigger—which is actually harmless—as a threat, and set the immune response into motion. There are several different methods of diagnosing allergies, including blood tests and skin tests.

This article will cover how allergies are diagnosed with skin tests and blood tests, as well as the advantages and disadvantages of both.

Skin prick allergy test
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How Allergies Are Diagnosed

Your healthcare provider may suspect allergies based on your symptoms and health history or a physical examination. The test they choose to diagnose allergies often depends on what type of trigger they think may be responsible for your symptoms.

If you have been taking antihistamines for your symptoms, you will likely need to stop taking them for a period of time before you can be skin tested.

Allergy Symptoms

Symptoms of allergies may include:

  • Skin rashes such as hives
  • Itching and redness
  • Sneezing
  • Runny nose
  • Sore throat
  • Itchy, watery eyes

Food allergies may cause other symptoms such as nausea, diarrhea, or other stomach issues.

Skin Test for Allergies

Procedure

Skin tests for allergies include skin prick testing, intradermal testing, and skin patch testing.

  • Skin prick testing: Skin prick testing can be used to identify allergies such as airborne allergies (pollen, mold spores) and food allergies. The procedure is typically performed on your back or forearm. The allergen is scratched lightly into the skin to see if you react to it. A positive test results in redness, itching, or raised round patches called wheals. This usually occurs within 15 minutes of placement of the allergen.
  • Intradermal testing: Intradermal testing is similar to skin prick testing in that a small amount of the suspected trigger is introduced to test for a reaction. However, the allergen is injected into the epidermis rather than scratched into the skin surface. Intradermal testing can be used to test for allergies to insect venom, penicillin, or medications. Your healthcare provider may choose to try intradermal testing if the skin prick testing was inconclusive.
  • Patch testing: In patch testing, a bandage, or "patch," that has the suspected allergen on it is placed on the skin and left there for roughly 48 hours. A healthcare provider will review the area after 72-96 hours to check for signs of a reaction.

Safety

Skin tests for allergies are generally considered safe. However, those who test positive may experience irritation at the site of the test (itching, hives, or slight pain from the scratch or needle stick).

While extremely rare, these tests could potentially cause an anaphylactic reaction in some people.

Anaphylaxis is a severe and life-threatening allergic reaction. Of the different types of skin testing, those that are performed in entirety at an office or clinic under the supervision of a healthcare provider are the safest, since those providers are trained to recognize and treat anaphylaxis.

Anaphylaxis

Anaphylaxis is a life-threatening allergic reaction that requires immediate emergency medical attention. Anaphylaxis can cause the throat to swell, which obstructs a person's airways, making breathing difficult. For severe allergies, a person should carry an injectable epinephrine device (EpiPen) at all times.

Cost

Skin testing is among the most affordable of tests used to detect allergies. The exact cost will vary depending on the healthcare provider and the type of test used. Most health insurance plans will cover this type of testing.

Contact your healthcare provider and insurance company, if you have one, for details regarding pricing prior to receiving the test.

Accuracy

False negatives are very unlikely with skin testing for allergies.

However, false positives occur about 50%-60% of the time with skin prick testing. For this reason your healthcare provider may order follow-up tests to confirm diagnosis.

Blood Tests for Allergies

Blood tests for allergies look for a certain type of antibody called immunoglobulin E (IgE), which the body produces once it becomes allergic to an identified trigger. This type of testing is also called RAST or ImmunoCap testing.

Procedure

Blood is drawn, typically using a needle and syringe, and then sent to a laboratory for analysis. The lab technician will add suspected allergens to the blood sample and see if IgE is produced in response to a specific allergen. Then IgE levels are measured.

Safety

Blood tests for allergies are extremely safe, with the only potential for any adverse reaction coming from the blood draw process (for example, pain or infection at the site of the needle stick).

Cost

This type of testing costs approximately $5-$20 per specific allergen tested (without insurance). The best way to determine your out-of-pocket cost is to contact your insurance provider (if you have one) or healthcare provider for pricing info prior to receiving the test.

Accuracy

Unfortunately, like skin testing, IgE testing also sees a high false positive rate at about 50%-60%.

Signs You Need an Allergy Test

It can be difficult to know if you have allergies, especially if your symptoms are similar to the common cold. But a cold typically only lasts a few days or weeks at most, while allergies persist.

You may need an allergy test if you have symptoms of allergies, such as skin rashes, hives, sneezing, congestion, sinus problems, or an episode of anaphylaxis. You may have noticed that these symptoms coincide with exposure to certain triggers.

Review your symptoms and medical history with your healthcare provider to determine if you need an allergy test and which type of testing would be best for you.

Summary

Skin tests and blood tests are two primary testing methods to diagnose allergies. Allergy tests are generally considered safe and affordable. A healthcare provider who is uniquely qualified to order these types of tests will perform them and determine the results. You may require more than one type of allergy test to help confirm a diagnosis.

A Word From Verywell

Allergies are extremely common and can interfere with your quality of life. Undiagnosed and untreated allergies can lead to conditions such as sinusitis and nasal polyps. Proper management of allergies depends on an accurate diagnosis, which can be achieved with the help of a qualified healthcare provider, such as an allergist.

Frequently Asked Questions

  • What are the most common allergies?

    The most common environmental allergies include pollen, dust, mold, cockroaches, and pet dander. The most common food allergies in the U.S. include milk, shellfish, nuts, soy, eggs, and wheat. Allergies to insect venom affect about 5% of the population.

  • Can you develop allergies as you get older?

    Yes, the immune system changes often throughout your life, so it's possible to both outgrow childhood allergies and to develop new allergies as an adult.

  • Is allergy testing typically covered by health insurance?

    Yes. As long as it is done by a qualified healthcare provider, most health insurance plans, as well as Medicaid and Medicare, cover allergy testing. You should contact your insurance provider before getting these tests to find out what out-of-pocket costs you may be responsible for.

7 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Asthma and Allergy Foundation of America. Allergy diagnosis.

  2. MedlinePlus. Allergy testing - skin.

  3. Food Allergy Research and Education. Skin prick tests.

  4. Plush Care. Allergy testing costs.

  5. Food Allergy Research and Education. Blood tests.

  6. Asthma and Allergy Foundation of America. Allergy facts.

  7. National Health Service. Allergies.

By Kristin Hayes, RN
Kristin Hayes, RN, is a registered nurse specializing in ear, nose, and throat disorders for both adults and children.