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How To Read Allergy Skin Test Results



What Happens If I Have An Allergy

Depending on the allergy, your healthcare provider may recommend one or more of these steps:

  • Minimize exposure to allergens: Avoid ones that cause severe reactions, such as latex or certain foods.
  • Take daily allergy medications: Antihistamines can prevent or reduce allergic rhinitis and other symptoms.
  • Get allergy shots: This type of immunotherapy can decrease the immune system’s response to certain allergens like pet dander. You should get allergy shots for three to five years to experience maximum benefit. Allergy shots can be costly, but they often provide long-lasting relief, even after the shot series is completed.
  • Have a medical alert card: A card or medical alert jewelry lets others know about your severe allergy. It tells them you could have an anaphylactic response to peanuts, bee stings or other allergens.
  • Carry an epinephrine injection: Keep this medicine with you at all times if you’re at risk for an anaphylactic allergic reaction.

A note from Cleveland Clinic

Allergic reactions can range from annoying congestion to life-threatening anaphylactic shock. Allergy tests can identify substances that cause these types of allergic reactions. There are different allergy tests. Your healthcare provider will choose the best test for you based on symptoms and potential allergy triggers. If you have allergies, you can take steps to get symptom relief.

How The Skin Allergy Test Is Performed

Allergy skin testing is usually done at a doctor’s office. A nurse generally administers the test, and a doctor interprets the results. Typically, allergy skin test takes about 20 to 40 minutes. Some allergy skin tests detect immediate allergic reactions, which develop within minutes of exposure to an allergen. Other allergy skin tests detect delayed allergic reactions, which develop over a period of several days.

There are three common methods of allergy skin testing.

How Do I Know If I Need An Allergy Test

If you’re allergic to allergens in the air like dust, pollen or pet dander, you may develop allergic rhinitis. Also known as hay fever, this allergic reaction causes:

Food allergy symptoms typically occur within 30 minutes of food ingestion but may occur up to two hours after ingestion. People with food allergies may experience:

  • Skin symptoms such as hives, swelling of the face, lips or tongue, generalized itching.
  • Respiratory symptoms such as coughing, wheezing, shortness of breath, chest or throat tightness.
  • GI symptoms such as nausea and vomiting, abdominal pain and cramps, vomiting and diarrhea.
  • Cardiovascular symptoms such as pale skin, weak pulse, dizziness or lightheadedness.

People who are allergic to latex, fragrances or metals like may develop contact dermatitis. This allergic reaction affects your skin. You may have:

  • Burning sensation on skin or .
  • Skin rash or itchy skin.

A patch test, performed by a dermatologist, is used to diagnose these types of reactions.

What Age Is Appropriate For Allergy Skin Testing

Per the American Academy of Pediatrics, age is not a barrier to skin testing. Even infants can benefit. As the child’s immune system develops, the child should be retested to identify changes in his/her immune response. Many times foods can be reintroduced into the diet that once caused an allergic reaction. In addition to Allergy & Immunology, our allergists train in either or internal medicine, so we are very comfortable treating pediatric patients for allergies and asthma.

Don’t keep suffering from allergies. Schedule an appointment today with one of our board-certified allergists.

Indications For Doing Skin Prick Testing

Table 4 from Allergy Testing.

Skin prick testing is most often used to demonstrate atopy. Atopy is characterised by an overactive immune response to environmental factors and has a strong genetic component. It usually manifests clinically as one or more of the characteristic disorders of asthma, , or hay fever . The results from skin prick tests can be used to guide the management of patients with asthma and hay fever, for example, to paln desensitisation to a certain allergen, removal of a family pet, removal of carpets, and avoidance of certain foods. It is also useful in patients with bee and wasp stings, and , especially if is being considered.

Skin prick testing is generally unhelpful in the investigation of , chronic urticaria and , food intolerances, dermatitis herpetiformis, and nonspecific rashes.

Overall, skin prick tests can provide confirmatory evidence for a diagnosis made on the patient’s history and clinical condition.

Different Techniques Quantifying Skin Prick Test Results

The outcome of the SPT can result in a variety of wheal shapes, as shown in Fig. . To determine the average diameter, the mean value of the longest and the midpoint orthogonal diameter of the wheal were measured . The area of the wheal was determined by using a flatbed scanner in combination with software earlier developed by Erasmus MC: Precise Automated Area Measurement of Skin Test . Mean values of two histamine-induced wheal sizes of the positive control were collected as well. Based on the measured data the HEP-indices were calculated for both the average diameter and area.

Fig. 1

Consequently the four readings were defined as:

  • 1.

    Average diameter .

  • 2.

    Area .

  • 3.

    HEP-index diameter .

  • 4.

    HEP-index area .

  • What Happens During An Allergy Skin Test

    You will most likely get tested by an allergist or a dermatologist. You may get one or more of the following allergy skin tests:

    An allergy scratch test, also known as a skin prick test. During the test:

    • Your provider will place small drops of specific allergens at different spots on your skin.
    • Your provider will then lightly scratch or prick your skin through each drop.
    • If you are allergic to any allergens, you will develop a small red bump at the site or sites within about 15 to 20 minutes.

    An intradermal test. During the test:

    • Your provider will use a tiny, thin needle to inject a small amount of allergen just below the skin surface.
    • Your provider will watch the site for a reaction.

    This test is sometimes used if your allergy scratch test was negative, but your provider still thinks you have an allergy.

    An allergy patch test. During the test:

    • A provider will place small patches on your skin. The patches look like adhesive bandages. They contain small amounts of specific allergens.
    • You’ll wear the patches for 48 to 96 hours and then return to your provider’s office.
    • Your provider will remove the patches and check for or other reactions.

    Skin Prick Testing Techniques

    Skin prick tests are usually performed on the inner forearm. Any number of allergens can be tested, as few as 3 or 4 or up to about 25 allergens. The following is a brief overview of how the test is performed.

    • Clean arm with soap and water or alcohol.
    • The forearm is coded with a skin marker pen corresponding to the number of allergens being tested. Marks should be at least 2 cm apart.
    • A drop of allergen solution is placed beside each mark.
    • A small prick through the drop is made to the skin using a sterile prick lancet. A new lancet must be used for each allergen tested.
    • Excess allergen solution is dabbed off with a tissue.
    • Observe skin reactions – if a reaction occurs it should do so within 20–30 minutes.

    In addition to the allergens tested, there should be a positive and negative control. The positive control, usually a histamine solution, should become itchy within a few minutes and then become red and swollen with a “weal” in the centre. The negative control, usually a saline solution should show no response.

    Allergy Blood Test Vs Skin Test

    Allergy blood tests are used to find out if you have an allergy. One type of allergy blood test called a total immunoglobulin E test measures the overall number of immunoglobulin E antibodies in your blood. Another type of allergy blood test called a specific IgE test measures the level of IgE antibodies in response to individual allergens.

    In allergy blood test, a health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.

    What do the allergy blood test results mean?

    If your total immunoglobulin E levels are higher than normal, it likely means you have some kind of allergy. But it does not reveal what you are allergic to. A specific immunoglobulin E test will help identify your particular allergy. If your results indicate an allergy, your health care provider may refer you to an allergy specialist or recommend a treatment plan.

    Your treatment plan will depend on the type and severity of your allergy. People at risk for anaphylactic shock, a severe allergic reaction that can cause death, need to take extra care to avoid the allergy-causing substance. They may need to carry an emergency epinephrine treatment with them at all times.

    Study Design And Patients Characteristics

    This study included a total of 172 children . All patients underwent a SPT with cashew nut extract and a DBPCFC test with cashew nut. The mean age of the children was 8.8 years , with 102 boys and 70 girls . Symptoms consistent with eczema were reported by 65 children , with asthma by 52 children and with hay fever by 89 children . Medical ethical approval was obtained and all patients signed informed consent.

    Allergen Skin Tests Are Generally Low Risk And Without Significant Side Effects But Rarely A More Severe Reaction Can Occur So It Is Important To Be Tested In An Appropriate Medical Setting

    Most often, allergen skin tests result only in mild localized itching and swollen bumps where tests are positive. These symptoms go away on their own within the day, and sometimes an ice pack, a topical steroid, or an antihistamine may be helpful. Less often, a delayed reaction can occur at one or more of the test sites after you have left the office, resulting in an area of swelling, tenderness, redness, and possibly itching that can last for several days. Rarely, introduction of allergens into the skin can produce a severe immediate allergic reaction that requires treatment immediately, which is why it is important to have your skin tests performed in the office.

    Selecting Allergens For Testing

    Regardless of whether a skin test or in vitro test is used, it is important to select allergens to be tested for based on the patient’s history and the need to identify which allergens are relevant for that patient. In the primary care setting, in vitro tests are the most common allergy test used. Many laboratories offer panels of allergens from which the physician can select. These are provided as a convenience, particularly if the physician is not familiar with the individual allergens and wants to order a panel that represents aeroallergens common to a particular region. Even so, it is not necessary to select a panel if measurement of IgE to selected allergens would be more appropriate for a particular patient.

    In general, patients with respiratory diseases such as rhinitis and asthma should have IgE measurements for aeroallergens which are more likely to be associated with their symptoms. Food-specific IgE tests should be reserved for individuals who have symptoms after eating a particular food. When there is a suspicion that symptoms are related to a food, but it is not clear which food among several is responsible, measurement of IgE to a limited panel of foods may be helpful.

    Ige Specific Blood And Skin Test Work Identically

    Table 1 from Allergy Testing.

    Contributed by Anke Tillman

    A RAST is a way of measuring the amount of IgE antibody in the blood stream made against a specific allergen. RAST tests and allergy skin tests give similar information. Both identify IgE antibody against materials you might be allergic to. RAST tests must be done by specific methods to be accurate and therefore must be sent to specific laboratories. RAST tests and skin tests each have their advantages and disadvantages. Skin tests may pick up some allergies that would be missed by RAST tests but skin tests have a small risk of precipitating an allergic reaction.

    RAST tests report IgE made against specific foods in units known as KU/L. Higher levels indicate a higher chance you will have a reaction if you eat the food. Lower levels indicate a lower chance you will have a reaction.

    Traditionally RAST TESTS have been reported as CLASS 0 to CLASS 5 or 6. Class 0 indicates no allergy. Class 5 or 6 indicates high allergy

    CLASS 0 CLASS 1 CLASS 5 CLASS 6

    The significance of a result varies with the degree of reaction on the test and with the food. For some foods the predictive value of the RAST test is very high, for others it is lower and not as clear cut as we would like it to be. At times, additional skin testing and in office challenges are required to clarify the significance of a test.

    Examples of RAST test significance include:

    Egg RAST greater than 7KU/L indicates a 98% chance one will react when eating eggs .

     

    Different Techniques Of Interpreting Skin Prick Test Results

    As a first step of assessing the different techniques of interpreting the SPT results, a comparison is made between the common-used average diameter method and the scanned area method . These two methods are compared in a scatterplot in Fig. . Every dot represents one patient. The dotted line shows the trend line of the data.

    Fig. 3

    Average diameter versus scanned area . A comparison is made between the common-used average diameter method and the scanned area method. Every dot represents one patient. The dotted line shows the trend line of the data. The lower bound value for ? is 1 is shown by the red line. The upper bound value for ? is 6.67 is shown by the grey line

    Pros And Cons Of Allergy Blood Tests

    Advantages of allergy blood tests include:

    • Can be done at any time, regardless of any you are taking
    • Requires only one needle stick ; this may be more attractive for people who are afraid of needles. Allergy blood testing is the preferred test for infants and very young children.

    Disadvantages of allergy blood tests include:

    • More expensive than skin testing; many health insurers do not cover allergy blood tests.
    • May be less sensitive than skin tests
    • Takes days or weeks to get results because the blood sample must be sent to a laboratory for evaluation; skin testing provides immediate results.

    There Are Two Main Types Of Allergen Skin Testing Used To Help In The Evaluation Of Potential Allergies Skin Prick Testing And Intradermal Testing

    Skin prick testing is minimally invasive and involves pricking the outer surface of the skin with either a commercial allergen extract or the fresh allergen if needed. Intradermal testing is slightly more invasive and involves a small injection of a solution containing allergen that is placed just underneath the surface of the skin.

    These skin tests are done on areas of the body that generally contain a substantial number of allergy cells, such as the arm or the back, and they are read for results during your appointment about 15-20 minutes after being placed. At Allergenuity Health, we attempt to be as least invasive as possible while getting the information we need to best help you with your goals.

    Patch Allergy Skin Test Procedure

    For a patch allergy skin test, there is no need to use needles instead the allergens are done on patches, the patches are then put into contact with the skin. About 20 to 30 different allergens that can lead to the contact dermatitis condition are tested. Some of these allergens include latex, drugs, fragrances, preservatives, hair dyes, metal, and gums.

    A person has to stay with the patch on their forearm or their backs for a period of 48 hours. They should avoid bathing or engage in activities that may lead to heavy sweating. The doctor removes the patch which may show some kind of an allergy.

    Allergy Skin Test Side Effects

    The most common side effects of skin allergy testing is slightly swollen, red, itchy bumps . These wheals may be most noticeable during the test. In some people, though, an area of swelling, redness and itching may develop a few hours after the test and persist for as long as a couple of days.

    Rarely, allergy skin tests can produce a severe, immediate allergic reaction, so it’s important to have skin tests performed at an office where appropriate emergency equipment and medications are available.

    What Is Done If A Skin Test Can’t Be Done

    For these patients, a doctor may use special blood tests, such as the RAST and the . These tests measure the presence of specific types of IgE in the blood.

    These tests may cost more than skin tests, and results are not available immediately. As with skin testing, positive RAST and ELISA tests do not by themselves necessarily make the final diagnosis.

    What Can I Expect After My Allergy Skin Testing

    Knowing what to expect after allergy skin testing can help you get back to your everyday life as soon as possible.

    How will I feel after allergy skin testing?

    A positive reaction can cause irritated, itchy and red bumps, similar to mosquito bites. Reactions usually go away in minutes to a few hours. Tell your doctor if you are uncomfortable or have allergy symptoms or other new or unusual symptoms. 

    When can I go home?

    You will likely go home right after allergy skin testing.

    When should I call my doctor?

    It is important to keep your follow-up appointments after allergy skin testing. Call your doctor fir questions and concerns between appointments. 

    Most allergy reactions occur while you are still at the doctor’s office for your test. Sometimes a delayed reaction can occur. Call your doctor right away if you have itching, swelling, or bumps on the skin testing area after going home. immediately for shortness of breath, mouth or , or difficulty talking or swallowing after skin allergy testing.

    What Is Allergy Testing

    Intradermal Skin Tests – Allergy Dog Central

    Healthcare providers perform allergy tests to determine whether your immune system overreacts to certain substances . If you have an allergic reaction, it means you have an .

    People can be allergic to things in the environment like mold, pollen and pet dander. Some people have allergic reactions to bee stings or . People with food allergies may not be able to tolerate peanuts, or .

    Will I Need To Do Anything To Prepare For The Test

    You may need to stop taking certain medicines before the test. These include antihistamines and . Your health care provider will let you know which medicines to avoid before your test and how long to avoid them.

    If your child is being tested, the provider may apply a numbing cream to his or her skin before the test.

    What Is Skin Allergy Test

    Allergy skin tests are used to find out which substances cause a person to have an allergic reaction. During allergy skin tests, your skin is exposed to suspected allergy-causing substances and is then observed for signs of an allergic reaction.

    Along with your medical history, allergy tests may be able to confirm whether or not a particular substance you touch, breathe or eat is causing symptoms.

    Information from allergy tests may help your doctor develop an allergy treatment plan that includes allergen avoidance, medications or allergy shots .

    Allergy skin tests may cause very mild discomfort when the skin is pricked. You may have symptoms such as itching, a stuffy nose, red watery eyes, or a skin rash if you’re allergic to the substance in the test.

    In rare cases, people can have a whole-body allergic reaction , which can be life threatening. This usually only occurs with intradermal skin testing. Your doctor will be prepared to treat this serious response.

    Allergy skin tests are generally safe for adults and children of all ages, including infants. In certain circumstances, though, skin tests aren’t recommended. Your doctor may advise against skin testing if you:

    Blood tests can be useful for those who shouldn’t undergo skin tests. Blood tests aren’t done as often as skin tests because they can be less sensitive than skin tests and are more expensive.

    What Is Allergy Skin Testing

    Skin testing is the most reliable form of allergy testing. Because mast cells are located in high numbers just under the skin, results of skin testing have proven to be more accurate than blood testing in diagnosing allergies.

    Please bring with you a complete list of all medications, as well as your pharmacy number and street address. We routinely send prescriptions electronically and need your pharmacy information to ensure accuracy.

    Your initial visit will take 2-3 hours in total. During the testing process, we will use a marking pen on your back and arms, which may cause staining on a shirt. For this reason, we suggest you bring an older shirt with you to wear home.

    How It Is Done

    The health professional doing the skin prick or intradermal test will:

    • Clean the test site with alcohol.
    • Place drops of the about 1 in. to 2 in. apart. This allows many substances to be tested at the same time.
    • Prick the skin under each drop with a needle. The needle passes through the drop and allows some of the allergen to penetrate your skin. For the intradermal test, a needle is used to inject the allergen solution deeper into the skin.
    • Check the skin after 12 to 15 minutes for red, raised itchy areas called wheals. If a wheal forms, it means you are possibly allergic to that allergen .

    Another skin prick method uses a device with 5 to 10 points , which are dipped into bottles that contain the allergen extract. This device is pressed against the skin of the forearm or back so that all heads are pressed into the skin at the same time.

    Medications Can Interfere With Skin Allergy Test Results

    Before scheduling a skin allergy test, bring your doctor a list of all of your prescription and over-the-counter medications. Some medications can suppress allergic reactions, preventing the skin testing from giving accurate results. Other medications may increase your risk of developing a severe allergic reaction during a test.

    Because medications clear out of your system at different rates, your doctor may ask that you stop taking certain medications for up to 10 days. Medications that can interfere with skin tests include:

    • Prescription antihistamines, such as levocetirizine and desloratadine .
    • Over-the-counter antihistamines, such as loratadine , diphenhydramine , chlorpheniramine , cetirizine and fexofenadine .
    • Tricyclic antidepressants, such as nortriptyline and desipramine .
    • Certain heartburn medications, such as cimetidine and ranitidine .
    • The asthma medication omalizumab . This medication can disrupt test results for six months or longer even after you quit using it .

    Are There Any Risks To The Test

    There is very little risk to having allergy skin tests. The test itself is not painful. The most common side effect is red, itchy skin at the test sites. In very rare cases, an allergy skin test may cause anaphylactic shock. This is why skin tests need to be done in a provider’s office where emergency equipment is available. If you’ve had a patch test and feel intense itching or pain under the patches once you are home, remove the patches and call your provider.

    How Long Does An Allergy Skin Test Take

    A person has to stay with the patch on their forearm or their backs for a period of 48 hours. This is for the patch allergy skin test. For the skin injection allergy skin test, the test is given fifteen minutes then observed for any allergic signs.

    • Allergy skin test list of allergens which are main or primary include allergens that are mostly inhaled. These affect the lungs or membranes found in the nostrils or throat, an example is a Pollen.
    • The second primary type is one that has to be ingested. They are known as ingested allergens and they are found in some foods e.g peanuts, soy, and seafood.
    • The third example is the ones that cause allergies by having to come into contact with a person’s skin. They mostly lead to itchiness and rashes. Such allergen is the poison ivy

    Allergy skin test results numbers are the numbers against which the results of the test are compared to in order to give the correct diagnosis.

    Allergy skin tests should be done by specialists only to prevent the side effects from being extreme and life-threatening. The tests are useful in determining the allergens that are harmful to a particular individual.

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