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Blood Testing For Allergies
Millions of Americans have allergies. You might sniffle and sneeze as the seasons change or get itchy and teary-eyed when you dust the house or pet an animal. Perhaps you start wheezing when you eat a particular food.
Allergy blood testing can help reveal what triggers your allergy symptoms and help your doctor choose the best treatment for you.
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 (IgE) 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:
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.
Other blood tests may be ordered that measure the release of chemicals responsible for allergic reactions.
Allergy skin testing is the preferred method, but in some cases blood testing may be ordered.
Allergy blood testing is recommended if you:
Blood tests for food allergies will look at environmental triggers. These blood tests aren't normally included in skin testing,
Your doctor may also order blood testing to determine how well your allergy treatments (immunotherapy) are working. Blood testing may also show whether you have outgrown an allergy.
Advantages of allergy blood tests include:
Disadvantages of allergy blood tests include:
These tests can be hard to interpret and are often reported as low to high-probability allergies. 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 (negative) 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.
Allergy blood testing is relatively safe. Side effects are usually minor and may include:
There is a potential that some people may faint during any type of blood testing.
Food Allergy Testing
A food allergy test is a skin or blood test that helps you and your doctor figure out if you're allergic to specific foods and which ones. Or if you think certain foods might be giving you or your child trouble, allergy testing can help you figure out what's going on.
First, see an allergist. They'll ask you questions about what you think you're allergic to and your symptoms. Sometimes that's enough to pinpoint the problem food, or the doctor may suggest some tests.
Allergy testing can help the doctor find out what you're allergic to, but it isn't foolproof. After your tests are done, you'll need to work together to get the right diagnosis.
The symptoms of a food allergy can be mild for one person and severe for someone else. Sometimes, they're even life-threatening. Common food allergy symptoms include:
Some people may also have a severe allergic reaction to food called anaphylaxis. Symptoms include tightened airways, throat swelling, a drop in blood pressure, and a fast pulse. You could pass out. If you think this might be happening to you or spot it in someone else, call 911 right away.
Skin testing is the most common and quickest food allergy test. Your doctor can test you for several foods at once.
First, they'll put a small drop of liquid containing the food on your skin and prick it. Then they'll watch for a reaction. It's usually a small bump that turns red. It might look like a mosquito bite.
If your skin reacts, you're probably allergic to that food. The doctor can talk with you about other treatment options. If you don't react, you probably aren't allergic to it.
Your doctor will take a sample of your blood and expose it to different allergens. You won't learn the results right away. This test is usually sent to a lab, and results could take a week or more.
Doctors don't use it as often. They may use it if they have an idea of what you're allergic to. That way, you don't have to be exposed to what may be the cause.
Neither skin nor blood tests can accurately predict how severe a food allergy reaction may be.
Doctors don't do this test often because it's dangerous for people with severe food allergies.
It's useful to confirm a skin or blood test, or to see if a child has outgrown an allergy. It can be used to eliminate a specific food from the list, too. Sometimes your skin might react to a food, but you wouldn't have symptoms if you ate it.
If a blood test doesn't find out what's triggering your symptoms, a controlled food challenge can help sort out the cause.
For this test, you'll go to your doctors' office or a hospital. That way doctors can watch you closely in case you have a severe allergy attack.
The doctor will give you food samples and watch for a reaction. Or you may take capsules -- some with an allergen in it, some without. That way the doctor can be sure it's the food causing the reaction.
Never try this type of test on your own. It can cause a serious reaction.
Food Allergy Testing 101: When It's Necessary And How It Works
Symptoms of a food allergy may start shortly after ingesting the food, or they may be delayed for a few hours. Common symptoms of a food allergy include:
If you or your child have symptoms of a food allergy, consider looking into food allergy testing. There are several ways to test for food allergies, including skin prick tests, blood tests, and oral food challenge tests. Doctors often use a combination of these methods to ensure an accurate diagnosis.
Food allergies vs. Food intolerance vs. Food sensitivityWhile often referred to interchangeably, food allergies, food intolerances, and food sensitivities are not the same, though some of their symptoms may overlap. Here's what they each mean:
Symptoms related to food sensitivities and intolerances aren't dangerous, but they cause discomfort and significantly affect your quality of life. Such symptoms can include diarrhea, bloating, stomach pain, and rashes.
Another difference between intolerances, sensitivities, and food allergies is that it may take only a trace amount of a certain food to trigger severe allergic reactions. Intolerances and sensitivity symptoms, on the other hand, are commonly dose dependent. This means a person will have a more severe reaction if a larger amount of the food is consumed.
While food allergies are most commonly diagnosed with allergy testing, intolerances and sensitivities are more difficult to diagnose and may only be identified through using elimination diets.
Most food allergies develop early in life, during childhood. Yet they can develop at any age, which means a food allergy could develop during adulthood. A food allergy will trigger some sort of symptom every time you eat the food or foods to which you're allergic.
Keep in mind that food allergy symptoms can vary in severity, and you may not have the same reaction every time you eat a food you're allergic to.
If you suspect you or your child may have a food allergy, it's critical to visit a healthcare professional, like an allergist, to undergo appropriate testing.
Several types of tests are commonly used to diagnose food allergies, including skin prick tests, blood tests, and oral food challenges. Here's a closer look at each.
Skin prick tests
After taking a detailed personal and family history, healthcare professionals typically use a skin prick test first when trying to diagnose a food allergy.
In general, skin prick tests provide a rapid means to detect food allergies and are cost-effective.
What to expect
Skin prick tests involve placing a small amount of liquid extracts of certain foods on your skin, usually on your back or arm. Next, the healthcare professional uses a small tool to lightly prick your skin, allowing some of the food extract to get below your skin's surface.
They may also test for nonfood allergens, such as pollen. This is because people allergic to pollen can also experience an itchy mouth and throat after eating certain fruits and vegetables, such as apples or kiwis.
The reaction occurs because the proteins found in these foods are similar to those found in pollen, which can confuse the immune system. Allergists refer to this as oral allergy syndrome or pollen fruit syndrome.
After 15–20 minutes, they'll examine the area for any signs of an allergic reaction, such as bumps or a rash.
Considerations
Though a positive test result indicates the possibility of reactivity to a food, it doesn't necessarily mean you have a food allergy. In fact, up to 60% of positive skin prick tests do not reflect symptomatic food allergy. So your doctor may have to use other tests, like an immunoglobulin E (IgE) blood test, to rule out or diagnose a food allergy.
Skin prick tests also aren't appropriate for everyone, including people who:
Blood tests
An allergy blood test measures the amount of IgE in your blood. There are two types of allergy blood tests:
Your healthcare professional might perform an allergy blood test after a skin prick test or when they cannot perform a skin prick test.
Blood tests may also be preferred over skin prick tests in young children, as skin prick tests may be too uncomfortable for them.
What to expect
To do a blood test, a healthcare professional will take a small sample of your blood and send it to a laboratory. In the lab, the sample will be exposed to different foods.
If your blood releases a lot of IgE antibodies in response to a particular food and you have symptoms when you eat that food, you're likely allergic to it.
Considerations
Unlike skin prick tests, which yield quick results, blood test results can take several days to get back. The test is also usually more expensive than a skin prick test, though some health insurance plans will cover the cost.
As with skin prick tests, blood tests can produce false positives. You may need to follow up with an additional test in the weeks or months after the initial one.
Oral food challenges
If skin pricks and blood tests don't produce clear results, your healthcare professional may have you do an oral food challenge. This is generally done in a doctor's office under close supervision, as it can sometimes cause a severe allergic reaction.
An oral food challenge is considered to be the most reliable and definitive food allergy test because it provides quick results that are easy to identify.
This test is also helpful for adults looking to find out whether they still have a food allergy from their childhood. For example, allergies to milk, eggs, wheat, and soy often resolve with age.
What to expect
To prepare for an oral food challenge, suspect foods are typically eliminated from the diet for 7 to 14 days before the challenge. This increases the likelihood of a definitive result. You must discontinue medications that could interfere with the results, such as antihistamines and b-adrenergic bronchodilators, before oral food challenge tests.
During an oral food challenge, you'll be given a small amount of food while your doctor checks for signs of a reaction. If you don't have a reaction, they'll gradually increase the amount of food. If you don't have a reaction to this larger amount, you can likely rule out a food allergy.
If the test result is negative, your healthcare professional will rule out a false negative with supervised feeding using a typical serving of the food in question. A false-negative oral food challenge result can occur in 1–3% of cases.
If an oral food challenge does detect a food allergy, you will have to completely remove the allergen from your diet to avoid allergic reactions.
Considerations
Unlike skin prick or blood tests, oral food challenges require avoidance of suspect foods for 7–14 days leading up to the test. Additionally, you could experience a severe allergic reaction during testing.
What about elimination diets?Elimination diets are sometimes used to help pinpoint specific foods that might be causing symptoms of an allergic reaction. They can also help confirm the results of skin prick or blood tests.
On their own, though, they can't be used to distinguish between a true food allergy and an intolerance or sensitivity, which are less severe.
During an elimination diet, you'll avoid eating certain foods for several weeks. Then, you'll slowly add them back in one at a time. Each time you reintroduce a food, you'll check for symptoms of an allergic reaction, such as:
It's best to keep detailed notes in a journal about what you eat each day and any symptoms you have. If you don't have any reaction to the reintroduced food, you can assume you aren't allergic or sensitive to it and move on to reintroducing the next food.
If you want to do an elimination diet, it's important to do it with the help of a healthcare professional, such as a doctor or registered dietitian, to avoid nutrient deficiencies, which can cause their own set of symptoms.
Yes, there are a variety of at-home food allergy kits you can order online or purchase in drugstores.
Most kits have you prick your finger and send a blood sample off to a laboratory. Other kits require sending in a sample of your hair. After analyzing your sample, the company will give you your test results.
At-home food allergy tests aren't generally recommended
Despite their widespread availability, many healthcare professionals do not recommend at-home allergy tests because of concerns about safety and reliability.
For example, most tests are based on outdated and questionable research and use controversial methodologies.
Food allergy testing generally relies on seeing whether your blood produces IgE antibodies in response to certain foods. But most home tests only measure immunoglobulin G (IgG) antibodies.
There's no evidence that this can help diagnose a food allergy. In fact, according to the American Academy of Allergy, Asthma, and Immunology (AAAAI), the presence of IgG in the blood is a typical immune response to food exposure, and having higher levels of IgG antibodies to specific foods may actually indicate tolerance, not an allergy.
A 2022 study found that just 1 of 22 food allergy test kit companies used an accredited laboratory, performed IgE testing, and had a clinician involved in the testing process. All of the other companies used unaccredited laboratories and controversial, unreliable testing methods.
It's also worth noting that while at-home tests may seem less expensive than a doctor's visit, most insurance plans don't cover at-home test kits. Because of this, your out-of-pocket cost may be higher with at-home tests, depending on your coverage.
A note on at-home food allergy testsThe AAAAI currently does not endorse the use of at-home allergy testing. Additionally, at-home food allergy tests cannot officially diagnose a food allergy. Instead, they can help identify foods that you have the potential to be allergic to.
If you're interested in at-home testing, the following three IgG-based tests passed Healthline's vetting process, have clinician involvement, and use accredited laboratories:
Still, keep in mind that if your results suggest that you may have a potential allergy, make an appointment with an allergist to ensure accurate interpretation and establish a follow-up plan.
There's no cure for food allergies, and the only treatment is strict avoidance of the offending allergen or allergens.
You must be aware of products that contain the food or foods to which you're allergic and be diligent about reading ingredient labels and making food workers, such as waiters, aware of your food allergy.
If you're allergic to multiple foods or are unsure of what products contain ingredients that might trigger an allergic reaction, it's recommended to work with a healthcare professional who specializes in food allergies, such as a registered dietitian or allergist.
They can help you identify products that contain allergens and develop an allergen-free, nutritionally complete eating pattern.
Your healthcare professional may prescribe medications, such as epinephrine and antihistamines, which people at risk for developing anaphylaxis should carry at all times. These medications are used in case of accidental exposure to an allergen and can save your life if you experience allergic symptoms such as throat swelling, shortness of breath, and low blood pressure.
In addition to providing medical advice and prescribing necessary medications, your healthcare professional can answer any questions you may have about how to keep yourself safe and healthy while living with a food allergy.
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