The RAST Method: In vitro allergy testing

The term in vitro refers to testing done outside of the body in a lab rather than directly on the body (as in allergy skin tests).

Dr. Alexander offers RAST testing, a type of in vitro testing for inhalant allergies. Inhalant allergies are allergies to substances such as dust, pollen, mold, animal dander, and mites that enter the body when you breath.

In vitro testing requires only a single blood sample and allows testing for many allergens. The test is very precise, indicating not only the allergens to which you are allergic, but also indicating "how" allergic you are to them. This allows Dr. Alexander to more precisely select dosages for allergy shots and other medications.

How it Works

People who suffer from allergies basically have overly alert immune systems that respond to substances that aren't harmful as if they were harmful. When your body is allergic to certain substances, it reacts similarly to the way it fights off a virus. A substance in the blood called immunoglobulin (IgE) recognizes allergens and attaches itself to them. In fact, a different type of IgE is produced for each substance your body is allergic to.

Having large amounts of a specific type of IgE may cause an allergic reaction when you breathe in the allergen — in other words, you are allergic to them. The more IgE you have for the allergen, the worse your reaction to it. The IgE attaches itself to a cell called the mast cell and forms an allergy "bomb" that is then triggered whenever you come in contact with its specific allergen. The bomb releases histamine, which is what causes the watery eyes, runny nose, congestion, and all of those other miserable symptoms you have with allergies. This is the body's attempt at flushing the allergen out.

The RAST test, which stands for Radio-allergo-sorbent test, combines a drop of blood with a drop of an allergen. If those allergen-specific IgE antibodies are in the blood, they willl attach to the allergen. A weak radioactive marker is added so that measurements can be taken for the amount of IgE antibodies in the blood. This measurement indicates whether you are allergic to that allergen or not. Since it only takes a drop of blood to do the test, many different allergens can be tested from the blood sample.

In most cases, you are only tested for the allergens you are most likely to come into contact with. This is based on your medical history, your symptoms, and other information you give Dr. Alexander.

Find out more about allergies.