What Types Of Tests Do Doctors Use To Diagnose Allergies
Skin Prick Test
Skin testing can confirm many common types of allergies. In some cases, skin tests can be the most accurate and least expensive way to confirm allergens. For prick/scratch testing, the doctor or nurse places a small drop of the possible allergen on the skin. They will then lightly prick or scratch your skin with a needle through the drop. If you are sensitive to the substance, you will develop redness, swelling and itching at the test site within 15 minutes. You may also see a wheal, or raised, round area, that looks like a hive. Usually, the larger the wheal, the more likely you are to be allergic to the allergen.
It is important to know:
- A positive skin test result does not by itself diagnose an allergy.
- A positive skin test does not predict the severity of an allergic reaction.
- A negative skin test usually means you are not allergic.
Intradermal Skin Test
In intradermal testing, the doctor or nurse injects a tiny amount of allergen into the outer layer of skin. The doctor checks your skin after a set amount of time for results, like with the skin prick test. Doctors may use this test if the skin prick test results are negative but they still suspect you have allergies. A doctor may use this test for diagnosing drug or venom allergy. At this time, there are very few indications for intradermal skin testing for food allergy.
Physician-Supervised Challenge Tests
Oral Food Challenge Test
The oral food challenge test is the most time intensive of all tests. Under the supervision of your allergist, your child will receive increasing doses of an allergenic food while be closely monitored for signs and symptoms.
You will be given specific instructions on the type of food to bring for testing depending on the allergen they are going to be evaluating. Some facilities will even have a specific recipe you will need to prepare to bring in for baked egg or milk challenges.
After your child consumes the food in increasing increments over an hour, the medical team will evaluate them for any signs or symptoms of an allergic reaction. If they experience anything significant, you medical team will be there to provide assistance and stop the test if needed.
Depending on the allergenic food, the OFC is used to help figure out if a a level of safe exposure can be offered at home to help the child outgrow a food allergy.
A standard OFC will generally yield accurate results, but the symptoms can also be delayed. For this reason, the OFC regulations require patients stay at least 2-3 hours minimum after the last food is tested to monitor for reactions.
For a deeper dive into the OFC research, I recommend taking a look at this 2019 study.
Results of OFC
While the method and record keeping may differ slightly amongst providers, here is a sample of both the peanut and baked milk OFCs my son underwent.
Baked Milk OFC
What Happens During The Apt
- First, we will use a special tape to place a prepared panel of food extracts on your back.
- You will be required to keep this panel dry, and in place on your back, for 48 to 72 hours.
- We will schedule a return appointment in our clinic so your allergist can remove the panel and obtain the test results.
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Rast Test Vs Skin Test
Different kinds of allergy tests are available, but the most commonly used is a skin or pinprick test.
In a skin test, small amounts of different allergens are placed on an individuals skin, usually with a pinprick. People who are allergic to these substances will develop itchy hives at these sites, while others without allergies will not.
The differences between the skin test and the RAST or ELISA blood tests are as follows:
- Speed of the procedure. Skin tests are faster than blood tests. A skin test can take place in the doctors office, but in a RAST or ELISA test, the medical professional must send a blood sample to a laboratory for testing.
- Speed of results. Reactions to a skin test typically develop within 15 minutes, whereas it can take between a few days and 2 weeks to get the results of a RAST test.
- Accuracy. Skin tests may be more sensitive than blood tests, though both methods are considered accurate for diagnosing allergies. It may be more difficult to interpret accurately skin test results on people with darker skin, and skin tests may be affected by medications while blood tests are not.
- Safety. Although it is rare, a person can develop a serious reaction to an allergen used in a skin test. There is no risk of this with a blood test, such as RAST or ELISA.
- Cost. A skin test costs less than a RAST or ELISA test to process, which may be a consideration for some people.
What Happens During An Allergy Test
Different types of allergy tests are used. Heres what happens during each:
Skin prick test: During this test, small amounts of substances to which your child may be allergic will be placed on your childs skin. Usually, the substances are placed on the forearm or back. Next, the skin is scratched or pricked. The skin is checked for a reaction at specific times.
Patch test: Substances to which your child may be allergic are applied to discs. The discs are then taped to your childs skin without eczema, usually on the back. Each disc contains a different allergen . Your childs skin be will checked at specific times for reactions.
Food allergy testing: A skin prick test or blood test can tell you what food allergies your child does not have.
If your child has a positive reaction to a food during one of these tests, the results must be confirmed with another type of test. Your childs dermatologist or allergist may refer to this type of type of test as a food challenge.
There are different types of food challenges. If this test is right for your child, the dermatologist or allergist can tell you what to expect.
Related AAD resources
ReferencesSidbury, R. Whats new in atopic dermatitis research? . In Lio PA , What’s boiling over: Atopic dermatitis and other eczematous conditions. Forum presented at the Summer Academy Meeting of the American Academy of Dermatology, Chicago, IL.
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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.
What Happens During The Spt
- First, we place a drop of liquid extract containing a small amount of the suspected food allergen on your forearm.
- Then, with a device similar to a plastic toothpick, we gently scratch the skin so that a tiny amount of the extract is absorbed.
- Over the next 10 to 20 minutes, we monitor the skin for a localized reactionredness, swelling or a measurable bump, called a wheal.
- Afterwards, we wipe off the skin and apply or administer antihistamine as needed. There is no bleeding, so you won’t need a bandage. SPT can be mildly uncomfortable for some people, but the discomfort is usually brief.
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Can You Allergy Test A Baby
In short, yes, you can allergy test a baby. Allergy testing itself can be done on someone of any age. That being said, its often recommended that it be done only when necessary with infants that are under six months.
As you can probably imagine, an infant under 6 months is still working on the important first steps of being alive. If a baby is under 6 months, a skin test will not be conducted. If an allergy test is absolutely necessary due to serious reactions, a blood sample test is often the method chosen by allergists.
Allergy Blood Test Results
A positive result means allergy-specific antibodies were detected in your blood. This is usually a sign of an allergy.
The blood test will reveal what exactly you are allergic to. However, you can test positive for something but never have had an allergic reaction to it.
A negative result means you probably do not have a true allergy. That means your immune system probably does not respond to the allergen tested. However, it is possible to have a normal allergy blood test result and still have an allergy.
Allergy blood test results should be interpreted with caution by an allergy specialist. Your doctor will also consider your symptoms and medical history when diagnosing a specific allergy.
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Allergy Testing For Kids: A Parent’s Guide
If your child suffers from allergy symptoms, your doctor may order blood or skin tests to make a diagnosis. Here’s what parents should know about the types of allergy tests available today.
Many parents recognize the signs of allergies in their children, including itchy eyes, runny nose, sneezing, and sore throat. And while the cause of allergies is often clear, sometimes moms and dads are left scratching their heads. Thankfully doctors can conduct allergy testing to pinpoint triggers and manage a child’s reactions.
To understand allergy testing, it helps to know what causes allergies in the first place. Your childs immune system produces antibodies to fight viruses, bacteria, and toxins. But sometimes their body reacts to a harmless everyday substancelike a bite of egg or dust particles in the airlike it’s a dangerous invader. If their body rejects pollen, for example, it might send chemicals to swell the lining of their nose, causing congestion and sneezing. Or if it’s something theyve eaten, the gastrointestinal lining gets inflamed, possibly leading to diarrhea.
To diagnose allergies, your child’s pediatrician may recommend you to an allergist who can conduct testing, says Sanjeev Jain, M.D., a board certified allergist and immunologist at Columbia Allergy. Allergy testing can be useful as a first step towards creating a plan to treat or reduce exposure to known allergens. Heres everything you need to know about the types of allergy tests available today.
Intradermal Test For Allergies
When It’s Used
If additional testing is needed, the allergist may recommend intradermal testing. Its useful for identifying potential environmental allergies, and it can also pinpoint some medication allergies, says Dr. Jain. It’s commonly used for detecting sensitivities to insect venom and penicillin.
Intradermal Testing Procedure
This test uses a small needle to inject potential allergens in a liquid form under the top layer of skin, usually on your upper arms or forearms. After the allergens are injected, the patient will wait for 20 minutes to see if a reaction occurs to the allergens applied under their skin, says Dr. Jain. Like with the skin prick test, an allergic reaction is characterized by an itchy red bump at the injection site.
Redness and itching usually accompany an allergic reaction. According to Dr. Jain, the itching will resolve in several hours, and it can be managed with an antihistamine or topical medication.
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What Is Food Allergy
Eating exposes the immune system to many different food proteins. The immune system learns to recognize and remember food proteins and typically considers them harmless. Food allergy happens when the immune system treats specific food proteins as harmful. Food proteins that can trigger allergic reactions are called food allergens.
The most common type of food allergy can develop when the immune system makes a type of antibody against certain food proteins. These antibodies are called immunoglobulin E and are also known as IgE antibodies. IgE antibodies interact with the cells of the immune system that contain inflammatory messengers like histamine.
When a person with food allergy eats their food allergen, IgE antibodies trigger a sudden, fast release of very large amounts of histamine and other inflammatory messengers into body tissues. These inflammatory messengers cause the inflammation that triggers allergic reactions. They can affect the skin, the respiratory tract , the gastrointestinal system and/or the cardiovascular system .
The signs and symptoms of an allergic reaction can include hives, swelling, wheezing, coughing, difficulty breathing, vomiting, faintness, weakness and passing out. The symptoms often come on quickly.
Signs Of Food Allergies
Food allergies can cause symptoms that can range from mild to life-threatening. Specific symptoms can cause:
- Skin problems, such as hives, itchy rashes or swelling
- Digestive issues, such as upset stomach, nausea, vomiting or diarrhea
- Respiratory problems, such as trouble breathing, wheezing, sneezing or throat tightness
- Circulatory issues, such as lightheadedness, pale skin or loss of consciousness
If your child has signs of a food allergy, see their health care provider. They may refer you to an allergist.
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What Is It Used For
Food allergy testing is used to find out if you or your child has an allergy to a specific food. It may also be used to find out whether you have a true allergy or, instead, a sensitivity to a food.
Food sensitivity, also called food intolerance, is often confused with a food allergy. The two conditions can have similar symptoms, but complications can be very different.
A food allergy is an immune system reaction that can affect organs throughout the body. It can cause dangerous health conditions. Food sensitivity is usually much less serious. If you have a food sensitivity, your body can’t properly digest a certain food, or a food bothers your digestive system. Symptoms of food sensitivity are mostly limited to digestive problems such as abdominal pain, nausea, gas, and diarrhea.
Common food sensitivities include:
- Lactose, a type of sugar found in dairy products. It may be confused with a milk allergy.
- MSG, an additive found in many foods
- Gluten, a protein found in wheat, barley, and other grains. It is sometimes confused with a wheat allergy. Gluten sensitivity and wheat allergies are also different from celiac disease. In celiac disease, your immune system damages your small intestine when you eat gluten. Some of the digestive symptoms can be similar, but celiac disease is not a food sensitivity or a food allergy.
Detailed Health History And Physical Exam
The health history and physical exam determines how likely a food allergy is the cause of a personâs symptoms after eating a food. The history also helps to identify which foods should be suspected. It is the most important step to a diagnosis because it helps to determine which foods to test, if any. Sometimes, the health history and physical exam will show that food allergy tests are not needed.
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How Can You Tell If A Child Is Outgrowing Their Food Allergy
Food-specific IgE antibody tests can be helpful for monitoring a child with food allergy. When a child is outgrowing their food allergy, the level of food-specific IgE antibody will be lower than what it was, but can still be positive.
For this reason, food allergy tests cannot confirm whether a child has outgrown their food allergy. The childâs doctor may suggest an oral food challenge to confirm that a food allergy has been out grown.
An oral food challenge involves eating the food allergen to see if an allergic reaction still happens. They are offered when there is a history of a severe reaction. Oral food challenges are only done in a medical clinic under the direct supervision of an allergist or pediatric allergist. If an allergic reaction happens, the allergist will be present to detect and treat it right away. Do not try oral food challenges at home.
Allergy Patch Test Or Epicutaneous Test
To diagnose allergies using an Allergy Patch Test, a doctor or nurse places some patches with different substances on the skin of the back. The test determines what allergen may be causing contact dermatitis. The doctor or nurse removes the patches after 48 hours, but the final reading is performed after 72-96 hours. If you are sensitized to the substance, you should develop a local rash. The number of patches depends on the suspected substances your doctor wants to investigate. Inform your doctor about all the medication you are receiving. Systemic corticosteroids or immunomodulators can change the results of the test. Baths and sweating can move the patches, so be careful.
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At What Age Is Allergy Testing Done
As mentioned above, there is no set age for someone to get allergy testing. Allergists, in choosing to recommend an allergy test or not, often will take a look a look at the child, the suspected allergen, and the reaction itself.
Since infants and children are often found to outgrow allergies, a lot of allergists will recommend waiting until late childhood to conduct a test if needed, especially if a parent is relatively certain of the suspected food .
If a child is having serious allergic reactions that are interfering with their health, school, or social life, or they are reacting to what appears to be a few allergens, an allergy test can be ordered at any age. So, at what age is allergy testing done? At whatever age, it is considered to be necessary for everyones safety.