How To Read Allergy Test Results
The thing that needs to be kept in mind is that these tests tend to be interpreted differently due to which comparing the numbers between them might not provide you with the clarity you are looking for. The common belief is that a higher number indicates that you are more sensitive to that particular antigen.
When we talk about RAST testing, the range differs from lab to lab depending on the techniques they use. The range can lie anywhere between 0.1 and 10 kU/L. The test revolves around measuring specific IgE levels that are directed toward the food in the blood.
These tests have low positive and high negative predictive value. It is quite common to encounter mild elevated results, particularly in children who have allergic conditions like asthma, eczema and allergic rhinitis.
The predictive values differ with every food item. However, it is said that the higher the level, the more chances there are of an IgE mediated allergy being present. Owing to false results, this is said to be a poor screening test.
Another test used for allergy is a physical supervised challenge test. In this test, the patient is made to consume an increased amount of suspected food allergen under the supervision of a physician.
If no symptoms occur which can be an indication of IgE mediated allergy, it implies that you are not allergic to that food item. The test tends to take around 4-8 hours but is found to be highly reliable.
Why Allergy Blood Tests Are Done
Allergy skin testing is the preferred method, but in some cases blood testing may be ordered.
Allergy blood testing is recommended if you:
- Are using a medicine known to interfere with test results and cannot stop taking it for a few days this would include antihistamines, steroids, and certain antidepressants.
- Cannot tolerate the many needle scratches required for skin testing
- Have an unstable heart condition
- Have poorly controlled asthma
- Have severe eczema, dermatitis, psoriasis, or another severe skin condition
- Might have an extreme reaction during skin testing or have a history of life-threatening allergic reaction called anaphylaxis
Your doctor may also order blood testing to determine how well your allergy treatments are working. Blood testing may also show whether you have outgrown an allergy.
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.
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What Happens If A Test Shows An Allergy
If your child does have an allergy, the allergist will work with you on a plan to keep your child safe. Youll learn how to help your child avoid foods that arent safe. The doctor also will give you a prescription for emergency medicine to keep with your child all the time in case of a severe allergic reaction.
Ige Specific Blood And Skin Test Work Identically
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 .
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How Is An Ige Blood Test Performed
An IgE blood test is done by inserting a needle into a vein in the arm or back of the hand, collecting a blood sample, and pulling it into a vial. The blood sample is sent to a laboratory to assess the response to different types of food allergens. Results can take a few weeks to become available. The results are given in numbers that range from 0.10 kU/L to 100 kU/L. Keep in mind that the results do not determine the severity of a reaction to a food allergen , only the level of antibodies produced after being exposed to the allergen.
What Is A Positive Skin Test Result
A positive skin test involves the formation of a bump and redness . In addition to the allergens in question, skin testing is also performed with a positive control that should always cause a skin reaction, and a negative control, , that should not cause a reaction. A test is positive if the allergen causes a wheal 3 mm greater than the negative control, and if the skin has a response to the histamine, as well. It is important to know that individuals cannot undergo skin testing if they are using antihistamines, since this blocks the histamine-mediated reaction.
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What Does A Positive Result Mean
Receiving a positive test result may not mean that you need to altogether avoid the allergen trigger for the rest of your life. In some cases, people can live healthy and comfortable lives despite exposure to their triggers.
A positive test result is mainly helpful because it allows you to pinpoint and avoid the allergen when possible. For instance, if you find out that youre allergic to pollen, you can then start trying to avoid going outside on days where pollen counts are high. If you find out youre allergic to dust mites, it might be time to wash your bedsheets.
Your allergen may also suggest taking medications such as antihistamines to help ease the symptoms of mild allergic reactions. These are especially helpful for environmental allergens like mold or ragweed that are more difficult to avoid than food or contact allergies.
Finally, allergy shots or another form of immunotherapy may be recommended to dilute the underlying causes of your allergies, rather than just the symptoms.
Immunotherapy works by gradually exposing you to an allergen over time so that your body can adjust. Sublingual immunotherapy is an FDA-approved method that requires nothing more than a tablet under your tongue over some time.
Why get injections when its as simple as that. Cleared makes fighting back against allergies quick, painless, and inexpensive with the lowest co-pay on the market. If youd like to find out if immunotherapy is right for you, take our free quiz.
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 doctors 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.
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Types Of Allergy Blood Tests
Allergy blood tests detect and measure the amount of allergen-specific antibodies in your blood. When you come into contact with an allergy trigger, known as an allergen, your body makes antibodies against it.
The antibodies tell cells in your body to release certain chemicals. These chemicals are what cause allergy symptoms. Immunoglobulin E is an antibody that’s strongly linked to the body’s allergy response.
Allergy blood tests usually screen for at least 10 of the most common allergy triggers, including dust, pet dander, trees, grasses, weeds, and molds related to where you live. They are also particularly helpful in diagnosing food allergies.
Allergy blood tests may be referred to as immunoassay tests and include:
- Enzyme-linked immunosorbent assay
- Radioallergosorbent test
The ELISA test measures the amount of allergen-specific antibodies in your blood.
The RAST test also looks for specific allergen-related antibodies in order to identify your allergy triggers. Since the introduction of the ELISA test, RAST testing has not typically been used.
Allergies can cause an increase in certain types of white blood cells. Blood tests to check your white blood cell counts, including a count of a type of white cell called an eosinophil, may also be done if your doctor thinks you have allergies. However, it is important to keep in mind that many other health conditions can cause an increase in white blood cells.
Do Allergy Blood Tests Ever Deliver False
About 50% to 60% of all allergy blood tests give false-positive results. False-positive results show you have an allergy even when you dont. Sometimes false positives happen if your body is reacting slightly to substances in certain foods youve eaten recently.
A note from Cleveland Clinic
An allergy blood test checks your blood for certain antibodies that increase if you have an allergy. Your healthcare provider might order one if you have a skin condition, take antihistamines or cant have a skin allergy test for any reason. Its important to remember that allergy blood tests often deliver false-positive results and they cant determine the severity of an allergy. If you have an allergy, talk to your provider about ways to reduce your risk of an allergic reaction.
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Blood Tests For Allergen Specific Ige
Immunoglobulin E antibodies directed against specific allergens can be measured with a blood test. These tests are often performed when skin testing is not easily available, when there is a skin condition such as severe eczema, or when a person is taking medications , that interfere with accurate skin prick testing.
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 persons 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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Are Skin Tests Safe
Skin tests are generally safe for most people, and they can even be done on children. Your allergist will monitor you the whole time as well, so if something goes wrong, youll be in good hands.
Many people who get skin tests say they feel minor discomfort during the prick itself, though its a non-invasive procedure that barely breaks the skin. The exposure to the allergen itself might cause you to feel itchy, get watery eyes, or even start sneezing.
In very rare circumstances, an allergy skin test may cause a severe allergic reaction known as anaphylaxis. This is a potentially life-threatening immune system response in which your body releases a flood of chemicals that causes you to go into shock. If this occurs, your allergist can administer a shot of epinephrine and get you emergency care immediately to help stop it.
Also, some skin tests can yield false positive results, meaning that the test indicates you are allergic to a substance even when you are not. This is most common when testing with food allergies because the way your body breaks down food proteins in the digestive tract is different from how it breaks down protein on the skin.
For that reason, it may seem like you have an allergy during a skin test even when youd be able to consume it without a problem.
Overall, though, skin tests are a great way to test for reactivity to certain allergens.
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.
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Benefits Of Skin Tests
Any allergy test is useful for being able to help you identify which substances might cause a reaction and which ones might be generally safe. But on top of that, skin tests carry some benefits that are advantageous over others.
For one, skin tests are extremely fast. In some instances, these allergy tests can detect a positive reaction instantaneously. However, the test usually doesnt last anywhere longer than 30-40 minutes.
Also, skin tests are pretty painless. The skin prick that occurs doesnt actually break the skin enough to draw any blood, so youll barely feel a thing. This is one of the advantages of skin tests over other ones like blood tests.
With that said, skin tests do yield quite a high number of false positives. In fact, its been found that 50-60 percent of skin tests produce false-positive results. Despite that, they are an extremely effective tool in helping to clear up any uncertainty surrounding what is and isnt causing your allergic reactions.
Reading Allergy Tests With Cleared
Allergy skin tests involve a tiny prick of the skin, followed by exposure to suspected allergens in the test area. Its goal is to show the severity and type of reaction to certain substances.
If youre allergic to a substance, it will form a bump called a wheal. Generally, the bigger or itchier the wheal, the more allergic to the allergen you are. This occurs because antibodies in your blood known as IgE antibodies interact with allergens and cause symptomatic reactions.
A reaction indicates a positive test result, but other factors like family history, medical history, and current medications can all play a role. If you find out youre allergic to something, youll likely be advised to avoid the trigger, take antihistamines, or consider immunotherapy.
Finally, if skin tests prove inconclusive or your allergist recommends you try another type of test, there are plenty to choose from. Patch tests, challenge tests, and blood tests are effective and can finally remove the mystery surrounding your stuffy nose.
To save a trip to the allergist and shield yourself from the pollen-filled outside world, meet your online allergist with Cleared. FDA-approved medications, licensed allergists, and personalized therapy have never been so accessible. Its time to finally take a breath of fresh air.
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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 systems 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 youre 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.
