This article will cover how allergies are diagnosed with skin tests and blood tests, as well as the advantages and disadvantages of both.
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.
Skin Test for Allergies
Procedure
Skin tests for allergies include skin prick testing, intradermal testing, and skin patch testing.
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 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.
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.
