Decoding Blood Allergy Tests: Procedure, Results, and Side Effects

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How accurate is the blood test for allergies?

Blood tests for allergies, such as the IgE test, are approximately 95% accurate. These tests measure the immune system's response to specific allergens and can accurately identify allergies in most cases. However, results can sometimes be influenced by factors like medication or recent exposure to allergens.

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What Are Blood Allergy Tests?

Blood allergy tests are diagnostic tools that measure the presence of specific antibodies in the blood, indicating an allergic reaction. These tests help identify the allergens causing your symptoms, aiding in appropriate treatment planning.


Blood allergy tests, also known as in vitro tests, are often used when skin tests are not an option. They can be particularly useful for individuals with skin conditions, those on certain medications, or those with a high risk of severe allergic reactions. These tests measure the presence of allergen-specific Immunoglobulin E (IgE) antibodies in the blood, which are produced by the immune system in response to an allergen. An elevated level of these antibodies may indicate an allergy.

Types of Allergy Blood Tests

The two primary types of allergy blood tests are the ImmunoCAP test and the Radioallergosorbent Test (RAST). The ImmunoCAP test is considered more sensitive and specific in detecting allergen-specific IgE antibodies, making it the preferred choice in most clinical settings. The RAST, although less commonly used now, can still be used to detect specific allergen reactions. These tests can help diagnose a broad range of allergies, including food, drug, insect venom, and respiratory allergies. Blood tests are also a suitable method for children as they are less invasive than skin prick tests.

Why Are Allergy Blood Tests Done?

Allergy blood tests are conducted to identify the specific allergens causing allergic symptoms. They help to diagnose allergies when skin tests are not suitable, and guide the development of tailored treatment plans for effective symptom management.

Allergy blood tests are often done when skin tests are not suitable, such as in individuals with skin conditions like eczema or psoriasis, or those who are on medications that can interfere with skin testing. They are also recommended for individuals who have a history of severe allergic reactions.

These tests measure the level of allergen-specific Immunoglobulin E (IgE) antibodies in the blood. The presence of these antibodies indicates that the immune system has reacted to a specific allergen. The results from an allergy blood test can help identify the allergens causing your symptoms, allowing for the creation of a personalized treatment plan. This could include allergy medications or immunotherapy, lifestyle changes, and avoidance strategies for specific allergens.

Allergy blood tests can also be a good option for children as they are less invasive than skin prick tests. They are also beneficial in cases where a broad range of allergens need to be tested, as they can screen for multiple allergens in a single blood sample. This makes them an ideal choice for comprehensive allergy testing, offering a clear picture of a person's allergic profile.

How Are Blood Allergy Tests Performed?

Blood allergy tests, also known as serologic tests, are performed in a lab setting with a simple blood draw. The blood sample is then analyzed for the presence of allergen-specific antibodies, which indicates an allergic response.

Procedure Details

To start, a healthcare provider will clean a site on your arm and insert a needle to draw a small sample of blood. The blood sample is then sent to a lab for analysis. While the procedure itself is quick, results can take a few days to a week.

In the lab, the blood sample is exposed to potential allergens and observed for the formation of Immunoglobulin E (IgE) antibodies. These antibodies are produced by the immune system in response to exposure to allergens. The quantity of IgE antibodies in the blood sample indicates the severity of the allergic reaction.

The advantage of blood allergy tests is that they can test for a wide range of allergens in a single sample. The results help to pinpoint the specific allergens causing symptoms, making it easier to formulate a personalized treatment plan. However, it's important to note that allergy blood tests can be more expensive than other types of allergy tests.

What Are the Pros and Cons of Allergy Blood Tests?

The pros and cons of allergy blood tests can vary depending on the individual's specific circumstances, their healthcare provider's recommendations, and the nature of their allergic symptoms. Understanding these advantages and disadvantages can help individuals make an informed decision about their allergy testing options.

Pros of Allergy Blood Tests

Allergy blood tests can detect a wide range of allergens from a single blood sample, providing a comprehensive overview of an individual's allergies. They are less invasive than skin tests, making them a suitable alternative for those unable to undergo skin testing, such as babies, people with severe eczema, or those taking certain medications. Additionally, unlike skin tests, blood tests are not affected by antihistamines and can provide consistent results regardless of recent medication use.

Cons of Allergy Blood Tests

On the downside, allergy blood tests can be more expensive than skin tests and may not be as sensitive in detecting certain allergies. The turnaround time for results is also longer, typically taking a few days to a week. While blood tests can provide an indication of allergic sensitivity, they may not replicate the body's actual response to allergen exposure as accurately as skin tests or patch tests. Therefore, they are often used in conjunction with other diagnostic methods for a more comprehensive understanding of an individual's allergies.

How to Understand Allergy Blood Test Results?

Understanding allergy blood test results involves interpreting the levels of specific allergen-specific IgE antibodies present in the blood. These levels are usually reported as a numerical value and can indicate the likelihood of an allergic reaction to a specific allergen.

The numerical value, often referred to as the IgE score, generally ranges from 0 to 6, with 0 indicating no specific IgE detected and 6 indicating a high level of allergen-specific IgE. A higher number usually suggests a greater likelihood of an allergic reaction. However, it's essential to note that the correlation between IgE levels and the severity of allergic symptoms is not always straightforward.

The interpretation of allergy blood test results should always be done by a healthcare provider, as they consider other factors such as the patient's history, symptoms, and physical examination. It's possible for individuals with high IgE scores to not experience any symptoms, and vice versa. Therefore, while the blood test provides useful information, it is not the sole determiner of an allergy diagnosis.

What Are the Side Effects of Allergy Blood Tests?

The side effects of allergy blood tests are generally mild and not long-lasting. Most commonly, patients may experience slight pain or bruising at the site where the blood is drawn.

While the needle prick itself is usually quick and causes minimal discomfort, some people may feel faint or lightheaded during or after the procedure. It's important to communicate with your healthcare provider if you're feeling unwell during the blood draw.

In rare cases, there may be more serious side effects such as infection, excessive bleeding, or an allergic reaction to the cleansing solution used on the skin. Always consult your healthcare provider if you notice any unusual symptoms after the test.

What Are the In Vivo and In Vitro Diagnosis Methods?

In vivo and in vitro are two primary methods used in allergy diagnosis. In vivo tests are performed on the person's body, while in vitro tests are conducted in a laboratory using the patient's blood sample.

In vivo tests include skin prick tests and patch tests. These tests expose the skin to potential allergens and observe for an allergic reaction. They are often used to diagnose food allergies, contact dermatitis, and respiratory allergies.

In vitro tests, on the other hand, RAST. These tests measure the presence of specific allergy-causing antibodies in the blood. They are particularly useful when skin tests are not feasible or safe.

What Is an Allergen Provocation Test?

An allergen provocation test is a diagnostic procedure that intentionally exposes a person to an allergen to observe and evaluate their reaction. It's often used when other allergy tests, such as skin tests and blood tests, do not provide definitive results.

The procedure varies depending on the type of allergy suspected. For respiratory allergies, allergens may be inhaled through a nebulizer. For food allergies, the suspected allergen is consumed under controlled conditions.

These tests should only be performed under medical supervision due to the risk of severe allergic reactions. Despite this, they offer a direct and effective way to confirm an allergy when other testing methods are inconclusive.

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Frequently Asked Questions

What allergies can be detected from a blood test?

A blood test can detect a wide range of allergies, including food allergies (like peanuts, milk, and eggs), mold, dust mites, animal dander, insect venom, certain medications, and specific types of pollen. The test measures the amount of allergic antibodies, IgE, in your blood.

What is a full panel allergy test?

A full panel allergy test is an extensive examination that screens for various allergens including foods, environmental factors, and animal danders. It typically includes skin prick tests, intradermal tests, and blood tests to accurately identify specific allergens causing allergic reactions in an individual.

How do you interpret allergy blood test results?

Allergy blood test results are typically quantified in units called kU/L. A result less than 0.35 kU/L indicates no significant allergy. Between 0.35 to 0.7 kU/L suggests a mild allergy, 0.7 to 3.5 kU/L is moderate, and over 3.5 kU/L indicates a strong allergic response.

Is IgG or IgE more accurate?

IgE tests are more accurate for diagnosing true allergies as they detect the antibodies your body produces in response to allergens. IgG tests, on the other hand, measure sensitivity to certain foods, but the presence of IgG can often indicate tolerance, not allergy.

What are the most accurate allergy tests?

The most accurate allergy tests are the skin prick test and the specific IgE blood test. The skin prick test checks for immediate allergic reactions, while the blood test measures the amount of IgE antibodies in your blood, which can indicate an allergy. Both tests should be interpreted by a professional.

What should you not do before an allergy blood test?

Before an allergy blood test, you should not stop taking any prescribed medication unless directed by your doctor. Also, avoid consuming alcohol, tobacco, or caffeine for at least 24 hours prior to the test. Always follow the specific instructions provided by your healthcare professional.

Is there a blood test for medication allergies?

Yes, a blood test known as the ImmunoCAP Specific IgE blood test can help identify a medication allergy. It measures the amount of certain antibodies produced in response to a drug, providing insights into possible allergic reactions. However, skin tests are more commonly used for this purpose.

What test is done for medicine allergy?

To diagnose a medicine allergy, doctors typically use a 'skin prick test' or 'intradermal test.' These tests involve applying a small amount of the suspected allergenic drug to your skin using a tiny needle. If you're allergic, you'll develop a skin reaction.

What is the treatment for blood allergy?

There's no specific treatment for a "blood allergy" because this term is not medically recognized. If you're referring to allergies diagnosed through blood tests, treatments might include antihistamines, corticosteroids, or immunotherapy. For accurate diagnosis and treatment, consult with a healthcare professional.

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