Allergy testing: Procedures and uses

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Allergies vary in triggers and responses, so there are several different tests a doctor may use to identify the cause of an allergic reaction.

The sections below outline some of these in more detail.

Skin prick test

The skin prick test is the most common method that doctors initially use when identifying potential causes of an allergy. It is simple, inexpensive, and quick, and it can test a broad range of allergens.

This method is useful when the predicted allergen, such as a seasonal allergy (hay fever) or a food allergy, has an immediate response.

The doctor will place a series of potential allergens along the person’s forearm, keeping space between each sample to prevent any overlap. They will then make a small prick in the middle of each sample, so that the allergen penetrates the outer layer of the skin.

If there is an allergic response, the skin may show signs of redness and swelling, producing a hive or wheal in the affected area.

The doctor will use a medical examination and information about a person’s history and geographic surroundings to select allergen samples for the skin prick test.

The skin prick test can identify allergens that cause:

• rhinitis
• asthma
• conjunctivitis
• eczema
• suspected food or drug allergies
• venom allergies following insect stings
• other, less common reactions

Intradermal test

An intradermal test is sometimes the next step when the skin prick method does not produce a strong result.

A skin prick test only penetrates the skin’s surface layer, but for the intradermal test, the doctor will use a syringe to inject the potential allergen under the skin.

Although the intradermal method is a very sensitive way to pick up allergens that may be causing allergic reactions, it is not a very specific test and often leads to false-positive results.

Patch test

A doctor may use a patch test when the suspected allergen has a delayed response. For example, they may expect a reaction after a couple of days rather than instantly. This is the case with contact dermatitis.

The doctor will place a patch containing a sample of the proposed allergen on the person’s back, where it will remain for about 48 hours. The doctor will then remove the patch and assess for an allergic reaction. They may do this again 2–3 days later.

If the skin has responded, it will likely be itchy and show signs of swelling and redness.

Blood tests

Blood tests are useful when skin tests do not work or other methods are unsafe or inconvenient.

The doctor will take a blood sample to complete serum immunoglobulin E (IgE) tests. During analysis, a health professional will extract serum IgE from the blood and assess it for an immune response against different potential allergens.

Challenge tests

A challenge test can sometimes identify the source of food allergies. This method is straightforward, but it should always take place under the close supervision of a health professional.

During a challenge test, a person will consume a small sample of a potential food allergen while the doctor watches for symptoms of an allergic reaction.

There are also allergy testing methods designed for use at home, but experts discourage the use of these.

The American Association of Allergy, Asthma & Immunology believe that home allergy testing kits are neither effective nor useful. Likewise, the World Allergy Organization discourage home testing with concerns that misdiagnosis is likely.

For example, it is easy to mistake intolerance for allergy when testing for an allergen at home.

A healthcare professional will have a better idea of which samples to test, based on the person’s history and the results of a physical examination.

Although experts do not recommend home testing kits, there are other options that can help. For example, a person can keep a diary of their exposure to things such as food or the environment and note when allergic symptoms occur.

In 2010, the National Institute of Allergy and Infectious Diseases supported the use of the elimination diet, wherein a person can try removing components such as gluten or lactose from their diet to identify what is triggering their potential food intolerance symptoms.

People should use this method carefully, to ensure that their diet remains balanced and does not lack vital nutrients.

Of the methods listed here, results from the blood test will usually take the longest to get back.

A doctor can use the results of an allergy test to work out a treatment plan. Treatment plans will vary between allergies and the severity of a person’s reactions.

Allergies are not usually preventable, so management often involves avoiding the allergen as much as possible.

In some cases, a doctor may prescribe medication, such as antihistamines or steroids.

Another potential treatment plan may involve allergen-specific immunotherapy, during which a person will have exposure to a small sample of the allergen over regular intervals to help their body get used to it.

Immunotherapy may take 3–5 years and can use several methods of exposure, including tablets and injections.

If recurring symptoms suggest an allergy, a person should see a doctor for an allergy test. They can determine the cause of the allergy and create a treatment plan to help alleviate a person’s allergic reactions.

Immediate medical attention is necessary if there is a sudden drop in blood pressure and a narrowing of the airways. This may indicate a state of anaphylactic shock, which is a potentially life threatening condition.

Allergic reactions occur when the immune system responds to harmless substances as though they are dangerous.

Allergies can cause uncomfortable symptoms, such as sneezing and hives, but the symptoms can be more severe, depending on the reaction.

There are several methods of identifying and treating allergens, but overall, it is best to seek professional help for diagnosis and treatment.