Allergy Blood Test Vs Allergy Skin Test: Whats The Difference
Allergy blood tests and allergy skin tests are two of the most common forms of allergy testing. During an allergy skin test, your healthcare provider creates tiny pinpricks in your skin and then applies an allergen to check for a reaction.
Skin tests deliver immediate results, but blood tests take a few days. Skin tests tend to be more accurate, but some people cant have allergy skin tests. If you have a skin condition such as hives or a rash, or youre taking antihistamines, allergy skin tests wont deliver reliable results. In these cases, you may need an allergy blood test.
What Types Of Allergy Tests Are Available
Allergy testing measures how a person reacts to specific allergens, such as tree pollen, pet dander, foods, medications or molds. A “positive” allergy test means that a person has a specific allergic antibody to the substance tested. This often means that the person is allergic to the substance, meaning that the person will experience symptoms when exposed to the allergen.
However, a positive allergy test does not necessarily mean that the person is indeed allergic to the substance. A person may have a positive allergy test to dog dander, for example, but experience no symptoms with exposure to dogs. In addition, a person may have multiple positive food allergy tests, but be able to eat these foods without any bad reactions.
Therefore, an allergist is needed to perform and interpret allergy tests based on the persons symptoms.
There are only two types of allergy testing considered to be valid: Skin testing and blood testing . Other tests for allergies may be performed in research settings , but are not helpful for everyday use. Patch testing is not used to test for allergy, but for contact dermatitis to various chemicals, which is caused by another part of the immune system.
What Basic Things Should You Know
The search for an trigger follows a sequence of steps: A skin test is usually done first, once you have talked with a doctor. A blood test is done instead if a skin test is too difficult or risky, or if the allergen in question isnt available in a solution that can be used in skin tests. Provocation tests are only considered if the skin test or a blood test havent provided clear results.
Before you have a skin test, it is a good idea to tell the doctor if you have any medical conditions affecting your lungs or skin, or if you have any cardiovascular problems. It is also important to mention any medication you are taking that may affect how your skin reacts, such as the amoxicillin or penicillin, or painkillers like acetylsalicylic acid or ibuprofen.
You should have no noticeable acute allergic symptoms right before doing a provocation test. Your doctor should be ready to respond quickly to any strong allergic reactions that may arise during skin tests, and particularly during provocation tests.
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What The Rast Shows
A negative RAST is as reliable as a negative SPT in ruling out a true food allergy. However, RAST has a slightly higher false positive rate than SPT, making it less reliable for confirming an allergy. If you have been diagnosed with a true food allergy, RAST can be useful in monitoring IgE values. If your RAST level falls below a given point, your allergist may recommend an Oral Food Challenge in our clinic, to determine if you still have an allergy.
Why Do Healthcare Providers Perform Allergy Tests
Your healthcare provider may perform an allergy test if you have allergy symptoms that bother you. Providers also perform allergy tests on people who have asthma. The test can identify allergy triggers that can worsen asthma symptoms or bring on an asthma attack.
You may also need a test if youve had a severe allergic reaction called anaphylaxis. This potentially life-threatening problem can cause hives or swelling, breathing difficulty and/or a sharp drop in blood pressure that brings on anaphylactic shock. Your health history along with allergy testing is used to determine the cause of severe reaction. If you have had an anaphylactic reaction or may be at risk for one, then you may need to carry an epinephrine auto-injector to treat the symptoms.
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Pros And Cons Of Allergy Blood Tests
Advantages of allergy blood tests include:
- Can be done at any time, regardless of any medications 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.
My Allergy Test Was Negative But I Continue To Have Symptoms What Else Could It Be
You could have an allergy-like condition that is not mediated by IgE for which there are no specific laboratory tests. You might have a genetic hypersensitivity problem, such as sensitivity to gluten with celiac disease or have an enzyme deficiency, such as a lactase deficiency causing lactose intolerance. It could also be another disease that is causing allergy-like symptoms. It is important to investigate your individual situation with your healthcare provider’s assistance. Test results alone cannot diagnose allergies, but rather confirm a diagnosis when circumstances suggest an allergy is likely. Results from any type of allergy test have to be interpreted along with your medical history by a healthcare practitioner who is trained to diagnose allergies specifically.
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Prick And Intradermal Allergy Skin Tests
Prick and intradermal skin tests are the norm for suspected seasonal, environmental, stinging insects, food, and medication allergies. During the test, the suspected allergen is positioned on the skin and evaluated after 15 minutes for signs of allergic reactions. While prick testing uses a pricking device to place the allergen on the skin, intradermal skin testing involves placing a solution containing the allergen just below the skin via a small needle.
Will My Allergies Ever Go Away
Although children do outgrow some allergies, adults usually do not. Allergies that cause the worst reactions, such as anaphylaxis caused by peanuts, do not usually go away. Avoidance of the allergen and advance preparation for accidental exposure, in the form of medications such as antihistamines and portable epinephrine injections, is the safest course. Immunotherapy can help decrease symptoms for some unavoidable allergies but won’t work for food and the treatment, which usually consists of years of regular injections, may need to be continued indefinitely.
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Blood Tests Vs Skin Tests
Both the blood test and the skin prick tests detect food-specific IgE. With the skin tests, the result is immediate, but the blood test result will take at least several days to arrive. Unlike the skin prick test, the blood test is not affected by antihistamines and can be performed for people with extensive rashes that prevent using skin tests.
Things To Keep In Mind
There are some important things to know about allergy shots. Testing positive to an allergen on a skin test does not, by itself, diagnose an allergy and does demonstrate the severity of the allergy. Testing negative on a skin test, usually means you are not allergic to that allergen.1 While the test showed that I was allergic to cats, dogs, and horses, it did not trigger the severe response that I had experienced prior to the test. Also, I tested negative to cinnamon, and I love cinnamon!
Allergy tests are uncomfortable, but they can tell us a lot about our allergies not everything though. There is no test that will tell you the severity of your allergy, but knowing what you are allergic to is just as helpful. If you are curious about different types of allergy testing and have more questions on how to proceed, contact your primary care physician or an allergist. If your allergies are affecting your asthma, the more you know the better you can protect yourself.
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How Is The Test Done
Suspected causes of allergy are mixed with liquid to make a solution. A drop of each solution is then placed on the skin – usually the forearm. Up to 10 or 12 drops of different solutions may be placed on the skin. The skin is marked to show which liquid has been placed where. Then, the skin beneath each drop is pricked with a very thin needle . This is usually painless, as just the very surface of the skin is pricked. However, this is enough to let a tiny amount of solution into the skin.
The skin is then observed for a reaction. If a reaction occurs, it happens within 20-30 minutes.
- A reaction is considered to be ‘positive’ when the skin under a drop of solution becomes red and itchy. Also, a white, raised swelling called a weal surrounds the red central area of any skin reaction. A weal takes about 15-20 minutes to reach a maximum size, and then fades over a few hours.
- A reaction is considered to be ‘negative’ when the skin remains normal. This means that you are not allergic to the substance in the solution.
Note: you should not take antihistamines on the day of the test, as they may dampen any allergic response during the test.
How Do Doctors Test For Food Allergies
How do doctors test for food allergies? Deborah
During skin prick testing, an allergy doctor or nurse puts a tiny bit of a liquid containing an allergen into the skin by making a small scratch or prick on the skin. Allergists usually do skin testing on a person’s forearm or back. The allergist then waits 15 minutes or so to see if a red, raised bump forms. If it does, there might be an allergy. The allergist will use a ruler to measure the wheal and the redness around it.
If someone might be allergic to more than one thing or if it’s not clear what’s triggering a person’s allergy symptoms the allergist may skin test for several different allergens at the same time.
Skin tests may itch for a little while, but this usually gets better after about 30 minutes. If your child is itchy after the test, the allergist might give them an antihistamine to take or apply a topical steroid cream to your childs back or arm to ease the itching.
A skin test that shows up as positive to a food only means a person might be allergic to that food. The allergist may request a blood test as well, sending a small blood sample to a lab for analysis. The lab checks the blood for IgE to specific foods. Again, if there are IgE antibodies to a food, it means the person might be allergic to it.
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How Do I Know If I Need An Allergy Test
If youre 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.
A patch test, performed by a dermatologist, is used to diagnose these types of reactions.
Blood Tests For Allergies
Skin testing is more common, but blood testing for allergies is also available. Typically, blood tests are recommended when patients cannot stop using antihistamines and other medications long enough for skin testing, when patients have dermatographism , or when patients skin has lesions or rashes that might interfere with skin testing. These blood tests, known as specific IgE tests or RAST tests, help evaluate a patients suspected allergies, much like skin tests but using a blood sample.
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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.
How The Test Is Performed
There are three common methods of allergy skin testing.
The skin prick test involves:
- Placing a small amount of substances that may be causing your symptoms on the skin, most often on the forearm, upper arm, or back.
- The skin is then pricked so the allergen goes under the skin’s surface.
- The health care provider closely watches the skin for swelling and redness or other signs of a reaction. Results are usually seen within 15 to 20 minutes.
- Several allergens can be tested at the same time. Allergens are substances that cause an allergic reaction.
The intradermal skin test involves:
- Injecting a small amount of allergen into the skin.
- The provider then watches for a reaction at the site.
- This test is more likely to be used to find out if you’re allergic to bee venom or penicillin. Or it may be used if the skin prick test was negative and the provider still thinks that you’re allergic to the allergen.
Patch testing is a method to diagnose the cause of skin reactions that occur after the substance touches the skin:
- Possible allergens are taped to the skin for 48 hours.
- The provider will look at the area in 72 to 96 hours.
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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.
Toxins Interacting With Proteins
Another non-food protein reaction, urushiol-induced contact dermatitis, originates after contact with poison ivy, eastern poison oak, western poison oak, or poison sumac. Urushiol, which is not itself a protein, acts as a hapten and chemically reacts with, binds to, and changes the shape of integral membrane proteins on exposed skin cells. The immune system does not recognize the affected cells as normal parts of the body, causing a T-cell-mediated immune response. Of these poisonous plants, sumac is the most virulent. The resulting dermatological response to the reaction between urushiol and membrane proteins includes redness, swelling, papules, vesicles, blisters, and streaking.
Estimates vary on the percentage of the population that will have an immune system response. Approximately 25 percent of the population will have a strong allergic response to urushiol. In general, approximately 80 percent to 90 percent of adults will develop a rash if they are exposed to .0050 milligrams of purified urushiol, but some people are so sensitive that it takes only a molecular trace on the skin to initiate an allergic reaction.
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Is Skin Prick Testing The Same As Patch Testing
No. Patch testing places substances on the surface of the skin. It aims to identify skin allergies. Skin prick testing checks for allergies that don’t necessarily occur on the skin, such as allergies to pollen, foods, etc. It is a way of getting the suspected allergen into the body and in contact with cells of your immune system to see if they react to it.
How Do Doctors Diagnose Allergies
Doctors diagnose allergies in three steps:
- Personal and medical history. Your doctor will ask you questions to get a complete understanding of your symptoms and their possible causes. Bring your notes to help jog your memory. Be ready to answer questions about your family history, the kinds of medicines you take, and your lifestyle at home, school and work.
- Physical exam. If your doctor thinks you have an allergy, they will pay close attention to your ears, eyes, nose, throat, chest and skin during the exam. This exam may include a lung function test to detect how well you exhale air from your lungs. You may also need an X-ray of your lungs or sinuses.
- Tests to determine your allergens. Your doctor may do a skin test, patch test or blood test. No one test alone is able to diagnose an allergy. Test results are just one of many tools available to assist your doctor in making a diagnosis.
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