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RAST testing

Understanding RAST-based Allergen Immunotherapy

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Allergen immunotherapy is the administration of specific allergens repeatedly to patients that are proven to have IgE-mediated allergies to protect against inflammatory reactions and allergic symptoms associated with the exposure to those allergens. It is a practice that has been going on for nearly a 100 years and has proved to alter naturally the course of allergic disorders like allergic asthma, allergic rhinitis, allergic conjunctivitis and hypersensitivity to insect venom like bee and wasp venom. Recently, this practice has been extended to treat allergies associated with food as well as atopic dermatitis.

When to go for Allergen Immunotherapy

Allergies not only affect the normal way of life to those affected but also cause life-threatening conditions. Taking allergy tests, whether skin tests or blood tests, help to identify specific allergens that are responsible for the allergic symptoms. This aids in the administration of drugs and better still help in avoiding those allergens. Sometimes, these allergic symptoms persist despite the use of medication or the allergens simply become unavoidable, and when this happens, there is another way out allergen immunotherapy. Allergen immunotherapy is recommended in situations where:

  • Medication doesn’t work
  • Medication has severe side effects
  • Allergy symptoms are so severe
  • Allergens are difficult to avoid
  • By people who want to avoid medication

RAST test

To understand the RAST-based immunotherapy, it is important first to look at the methods of testing allergies. Allergies are commonly identified using the skin test and blood (RAST) test method. Since the interest here is RAST-based immunotherapy, a quick look at the blood test method is important. In an allergic reaction, specific antibodies (IgE) are produced by specific allergens and to determine the presence of these allergens, serum from the patient has to be mixed with different allergens. The blood sample from the patient is added to allergens that are chemically bound to an insoluble matrix. In a positive reaction, the IgE will bind to the allergen after which a labeled anti-IgE is added that attaches to the bound IgE after which identification and quantification are done. This method not only identifies allergens but also shows the levels of hypersensitivity to specific allergens.

RAST-based allergen immunotherapy

Allergen immunotherapy involves a controlled exposure to already known allergens to reduce the severity of allergic symptoms or disorders. The process is usually long, and it can take up to six months to realize initial progress and up to 5- 6 years to see the full benefits. The process is about slowly allowing the immune system to tolerate allergens. At first, a small dose of the allergen is introduced and then it is increased overtime. When going for immunotherapy, it is necessary first to identify initial treatment doses that are considered safe, and this is where RAST scoring system becomes a reliable method to identify those dose levels.

RAST testing for allergens can quantify the levels of specific IgE that are produced in response to a specific allergen and allows for the selection of safe immunotherapy doses for each allergen. For instance, when the degree of hypersensitivity is low or moderate, the starting allergen concentrations to be administered is higher leading to reduced time and number of doses to be administered entirely. When the level of sensitivity is high, the starting concentration of allergen doses needs to be low due to the high caution that has to be taken.

Depending on the level of sensitivity to different allergens, the initial concentration dose to be given to each patient should be inversely proportional to the respective degree of sensitivity.

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Understanding Allergy Diagnoses


Allergies are a very common problem. One in five Americans have symptoms of allergies or asthma, and over half of people tested for allergies test positive for one or more allergies. Despite the commonness of allergies, it can be difficult to understand your allergy diagnosis.

Medical History and Symptoms

Your allergy diagnosis will begin with your doctor taking a medical history and asking you about your symptoms. They will also perform a physical exam to check for any common allergy symptoms.

Allergic Rhinitis

If your allergy symptoms involve a runny or stuffy nose and itchy eyes, you are most likely suffering from allergic rhinitis. These can include pets, pollen, dust, and mold. Your doctor may choose to treat you with medication and forego further testing. Your doctor may be able to tell you what you are most likely to be allergic to based on your symptoms and when they occur.

Drug and Insect Allergies

Drug allergies and allergies to insect stings can cause itching, swelling, hives, and anaphylaxis. Anaphylaxis is a life-threatening condition that can cause nausea, a severe drop in blood pressure, severe breathing difficulty, unconsciousness, and death. These allergies are easily identified because you will develop symptoms after being exposed to your allergen. If you are diagnosed with one of these allergens, you will need to take great care to avoid them.

Allergy Testing

Allergy testing is needed when a medical history and exam isn’t enough to make a diagnosis. They can be performed to diagnose any type of allergy.

Skin Prick Test

A skin prick test is an accurate way to diagnose most allergies, including those caused by environmental allergens, food, and contact allergies. The doctor will place a small amount of the allergen on your skin and prick or scratch it. If you are allergic to the substance, you will develop swelling, redness, and itching at the site within fifteen minutes. A positive test result means that you are likely allergic to the substance.

Blood Tests

Blood tests can be useful when you are taking medications to manage your allergy symptoms or you have very sensitive skin. The doctor will draw your blood. Then the lab will expose your blood to your suspected allergens. They then measure the amount of antibodies your body produces in response to the allergen.

Patch Test

The patch test is generally used when your doctor suspects that you have contact dermatitis. The doctor will place the allergen on your skin and apply a bandage. After 24-48 hours, the doctor will remove the bandage and check for any reaction. Redness and itching at the site means that you are allergic to the substance. The patch test can also be used with trays. The tray has small compartments that contain different allergens. This is an effective way to test for multiple skin allergies at once.


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How to Get to the Root of your Patients’ Allergy-Like Symptoms

Allergy is a very common condition that affects millions of people who are allergic to the things that they eat, breathe or touch. The problem with many people who experience allergy-like symptoms is that they rush to taking antihistamines without confirming if they have an allergy or not and what is it that they are allergic to. Others rely on free allergy screening and home test kit results to confirm their allergies. However, there are those who know the importance of seeing a doctor for their allergy-like symptoms, and when they do that, they expect you as the doctor to provide solutions to their problems.

Start with examination

Allergy –like symptoms can be caused by an allergy, several allergies or other things that are not related to allergies at all. As a doctor, you should be able to confirm an allergy suspicion, determine the responsible allergens or rule out allergy and the first thing your patient needs is not an allergy test but a doctor’s examination. The reason against relying on allergy tests alone is the risk of getting a ‘false positive’ result especially with free screening services offered by drugstores and supermarkets and home allergy testing kits. Your examination together with the medical history of your patient should confirm the suspicion of an allergy and also whether to proceed with an allergy test or not.

Making an accurate allergy diagnosis based on medical history, clinical observations and antibody testing is crucial because any wrong test can mean a waste of money and unnecessary lifestyle changes for your patient whose condition is far away from being an allergy plus the problem will not be solved in the long run.

If you suspect food allergies, you should recommend an elimination diet by identifying suspected foods causing the allergy symptoms and supervising it over a period. For the confirmation of other allergies, skin and blood allergy tests should be done.

Refer to an allergist to perform an allergy test

Doing allergy tests is usually done to know which substances are responsible for allergy symptoms. You can order either skin or blood allergy test depending on the nature of the symptoms.

Skin allergy test

If your patient exhibits allergy symptoms like the ones associated with food allergies, allergic rhinitis, asthma, skin rashes, angioedema, hives, venom and penicillin and related drugs allergy, skin tests may be done either by a prick test or intradermal skin test for venom and penicillin allergy tests. Before a skin test, you will need to prepare your patient in advance concerning the medicines that should not be taken like antihistamines because they influence the results of the allergy skin tests. Skin tests usually involve placing several suspected allergens on the skin and then the skin is pricked for the allergen to go under the skin. The skin is then watched for reaction signs for about 15-20 minutes.

Blood allergy tests

You should be able to order an allergy blood test if your patient is using antihistamines, has a severe skin condition, has a heart condition and unable to tolerate skin scratches or needles as in children. In allergy blood tests, either an ELISA test which measures the quantity of allergen-specific antibodies (IgE) in your blood or RAST test which looks for allergen-specific antibodies to identify the allergen is used.

Whatever the type of allergy test that you do on your patient, it should help you in knowing the root cause of allergy symptoms that your patient is experiencing. A negative result rules out allergy while a positive result means that the patient is allergic to that particular substance.

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How to Identify Allergy Triggers

Diagnosing patients with allergies isn’t as easy as it seems, but it is generally simple. While allergy triggers can vary, the processes for diagnosing the exact allergy are fairly straightforward. Some can be done by the patient at home but take time, while others need laboratory evaluations but are fairly fast. Here’s a look at five ways to identify allergy triggers.


This is usually used for potential food and skin allergies. The patient needs to start eliminating various foods and cosmetics/cleaning substances from his or her life, gradually adding them back in. For example, someone who has noticed a rash popping up more often after the person eats shellfish needs to eliminate all shellfish, any derivatives from shellfish, and anything that could be contaminated by shellfish for several days (10 days to 2 weeks is a common time period). If the rash clears up, the patient adds one specific food back in and waits another few days to see if the rash comes back. As you can see, this can take a long time and be easily derailed if the patient accidentally eats one of the test foods at the wrong time.

Location and Season History

This is a fairly simple procedure, but it takes a long time. Basically, the patient has to notice when and where the allergy occurred. Sometimes the result is inconclusive, and the patient has to have more specific tests done. But many times, the patient can quickly figure out if the problem has to do with a pet, a dwelling (e.g., one with a mold problem), or a seasonal pollen. This method will not distinguish between true allergic rhinitis and vasomotor rhinitis, but it can show the patient what he or she needs to avoid.

Skin Prick Test

This is the basic lab test done for allergies initially and is read by the doctor or nurse in the same lab or office. Note that it works for IgE-based allergies only. It can test for food, medication, and environmental allergies — pretty much anything that can be turned into an extract or administered via needle. A small amount of the suspect substance is placed just under the top skin layers with a needle, along with a glycerin control test spot. The reaction of the skin to the substance, and that reaction compared to the reaction to the glycerin, tells you whether an allergy is present. Note that hidden skin conditions like dermatographia can make this difficult; if the person reacts to the glycerin, too, the test becomes unreadable.


This is a blood test given when skin tests are not readable or doable. A blood sample is used to detect antibodies to allergens. The blood sample is not tested immediately unless there are no other tests in line for evaluation, so it can be a couple of days before results show up. This is another IgE-only test.

Biopsy and Other Invasive Tests

For allergies caused by antibodies other than IgE, a biopsy or other invasive test may need to be done.

Whether you send RAST samples out to another lab or have an attached lab department with techs who can administer skin prick tests, having a good lab that can accurately evaluate test results is crucial when it comes to allergies. Ensure that your patients receive the correct diagnosis by choosing your lab carefully.

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Why You Should Perform RAST Testing Before Prescribing Antihistamines

Radioallergosorbent test (RAST) is a method of measuring the amount of antibody IgE that is produced by the immune system as a result of exposure of your blood to a particular allergen. It is true that allergic reactions or disorders are among the most common problems encountered in emergency medical care. Such disorders include rhinitis, asthma and conjunctivitis as well as other allergic reactions towards food, drugs and insect venom. In as much as allergic reactions are common, it is not advisable for you to start using antihistamine drugs at any allergy-like symptoms that you encounter. It is a fact that majority of symptoms that resemble allergies are may not be true allergic reactions. It is, therefore, paramount for you to perform RAST testing before taking any antihistamines for the following reasons:

For correct diagnosis

Given that many symptoms that resemble allergies are not a result of allergic reactions, it is important to confirm by testing if your condition is as a result of an allergy or other medical conditions. If you are to take antihistamines without this confirmation, you will not have provided the correct solution to your problem and the situation is likely to become even worse. You should be able to consult a physician who will conduct an RAST allergy test or a skin prick allergy test. A RAST test is better because it is not sensitive, require no special preparations, is safe when you have other medical conditions like skin disorders, it does not require you to stop the use of antihistamine resembling drugs, creams or moisturizers for some time before the test is done and it can be used for small children who cannot tolerate skin pricking. Read More

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