Definition

The IgE test measures the level of IgE, an immunoglobulin, present in the bloodstream. IgE is a protein produced by the immune system as part of its response to substances that can harm the body. These substances could be allergens, parasitic infections (like worms), or diseases that affect the body's immune defenses.

There are two types of IgE tests:

• Total IgE test: This test measures the overall level of IgE in the blood, providing a general picture of the immune system’s activity.

• Specific IgE test: This test identifies the specific IgE produced in response to particular allergens (substances that cause allergic reactions). It is particularly useful in diagnosing allergies.

Typically, doctors recommend the specific IgE test when they suspect that a patient may have allergies. In contrast, the total IgE test cannot definitively confirm the presence of allergies because an elevated total IgE level can also indicate parasitic infections or immune system disorders. Both tests require blood samples, and they can either be performed separately or together using the same sample.

Indication

IgE tests, both total and specific, are recommended for several health conditions, including:

• Allergies

• Allergy-related conditions: Such as rhinitis (nasal inflammation) or asthma

  • Chronic respiratory symptoms that last for a long time

  • Skin reactions, like redness, itching, or hives

• Severe allergic reactions, such as anaphylaxis

• Parasitic infections

• Autoimmune diseases, when the immune system mistakenly attacks the body’s own cells

• Monitoring treatment success

Specific IgE tests are especially useful in identifying triggers for chronic allergies, where the exact cause remains unknown. This test helps pinpoint the specific substances (such as foods or inhaled particles) that trigger allergic reactions by measuring the levels of IgE produced in response to them.

Contraindication

For the IgE test, there are no absolute contraindications, meaning that there are no specific conditions that completely prevent someone from undergoing the test. However, there are several considerations to keep in mind when deciding whether to have an IgE test:

• The IgE test is not recommended for monitoring recurring allergic reactions.

• The specific IgE test using food allergens is not recommended unless typical symptoms of an allergic reaction to food are present.

• The specific IgE test involving food allergens or inhaled compounds should not be performed on patients who experience hives unless there is a known history of hives triggered by food or inhaled substances.

It's also important to note that specific IgE tests that use food ingredients as triggers can be quite expensive. Therefore, these tests should only be carried out when there are clear indications for their use.

Preparation Before the Test

No special preparations are required before undergoing the IgE test. However, it is essential to inform your doctor and healthcare providers about any medications you are currently taking, as some drugs may affect the test results. Additionally, if the test is being conducted on a child, it’s helpful to prepare them by explaining the process in simple terms. You can tell them that the IgE test involves drawing blood with a syringe, and though there may be a brief moment of discomfort, it will only last for a short time.

Test Procedure

The IgE test involves taking a small blood sample from a vein, typically in the arm, and is performed as follows:

• The healthcare provider will clean the area of skin where the blood sample will be taken using alcohol swabs.

• An elastic band will be wrapped around the arm to increase the size of the veins, and the patient will be asked to clench their fist to make the veins more visible and accessible.

• Once the vein is located, a needle will be inserted into it, and blood will be drawn into a syringe or tube.

• After the sample is collected, the elastic band will be removed, and the injection site will be pressed with alcohol gauze to stop any bleeding.

Following the procedure, patients may experience mild pain at the injection site, and some may develop bruising, though this is generally temporary. The collected blood will be analyzed to measure the total IgE levels in the bloodstream.

For the specific IgE test, the procedure is the same, but the patient will first be exposed to allergens (substances that could trigger allergies). After exposure, blood will be drawn, and the levels of specific IgE will be analyzed to determine the body’s reaction to the allergens.

Normal and Abnormal Values

Normally, IgE levels in the blood are very low or even undetectable. However, in cases of allergies, infections, immune system disorders, or certain cancers, IgE levels can be elevated. The following are the typical reference ranges for total IgE levels based on age:

Any IgE levels that exceed the maximum limit for a given age, as shown in the table above, are considered abnormal. For the specific IgE test, normal levels are below 0.35 kU/L, while levels above 3.50 kU/L are considered elevated.

Results and Recommendations (Follow-up Tests)

Elevated total IgE levels that surpass the normal range can be an indicator of various medical conditions, such as allergies, infections, immune system disorders, or even certain types of cancers. However, it's important to note that total IgE levels alone are not sufficient to make a definitive diagnosis. The doctor will consider the total IgE test results alongside your symptoms and medical history. Additional tests will be necessary to confirm a diagnosis and further investigate the underlying cause of your symptoms.

In the case of the specific IgE test, if the results are in the high range, it suggests that the substance or allergen used during the test triggered a significant allergic reaction in the body. Specific IgE levels that fall into a very high category should be taken seriously, as they indicate a stronger immune response and potential risk for severe allergic reactions.

Consult the Right Doctor

If you undergo both total and specific IgE tests and the results are abnormal as described above, it is essential to consult with an internist, particularly one who specializes in allergies and immunology. They will evaluate the results and determine the appropriate next steps. This may include additional tests, therapies, or treatment plans designed to address the underlying condition and manage the symptoms effectively.

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