Allergy sufferers know all too well their symptoms: sneezing, coughing, runny nose, and itchy eyes, nose and throat. They usually don’t know what exactly is causing those symptoms. Allergy testing is the first step toward evaluating and managing allergies and asthma; and it can be accomplished in two ways: skin testing and blood testing, which is often referred to as RAST allergy testing.

RAST Allergy Testing

RAST is short for radioallergosorbent, a brand name adopted by the Swedish firm that developed the method in the 1970s. Blood samples are collected at a lab and results are usually available in a few days. The sensitivity of blood testing compared to skin testing varies widely, but the average is between 70-75 percent.  For this and other reasons, RAST allergy testing is usually only recommended for uncooperative patients, those with extensive skin disease or food allergies, those unable to even temporarily discontinue the use of antihistamines, and in situations in which history suggests a high risk of anaphylaxis (a severe and rapid-onset allergic reaction) from skin testing.

How Skin Testing Works

Like RAST allergy testing, skin testing reveals the existence of a specific allergic antibody called Immunoglobulin E. The skin of the upper back or forearm is cleansed with rubbing alcohol then pricked with devices containing specific allergens. These include airborne allergens, such as pollens, molds, dust and animal dander; the venoms of fire ants, wasps, yellow jackets, bees and hornets; as well as antibiotics and penicillin. Testing is done in the office and results are available during the same appointment.

Skin tests are conducted using a variety of devices, however none has been shown by studies to be superior to the others. More impactful are how well the technicians are trained and how closely the instructions on the test package are followed.

Why Skin Testing is Preferred

Allergy skin testing is simple, quick, and easy to perform. It is low cost and has high sensitivity. All of this makes skin testing preferable to blood testing for the diagnosis of IgE mediated diseases. If a provider doesn’t offer skin testing, blood testing is considered an acceptable alternative to determine the appropriate therapy for the allergic patient. But given the choice, choose skin testing.