IgE class levels provide an indication of the severity of a suspected allergy. For a patient exhibiting symptoms of an allergic reaction, two types of blood allergy tests exist: the radioallergosorbent, or RAST, and the IgE antibody or enzyme-linked immunosorbent assay test, also known as ELISA. Different from allergy skin tests, these blood tests help decipher the levels of antibodies present in the blood when subjected to an allergen. Understanding levels of IgE facilitates diagnosis and treatment.
According to Marshfield Labs, class levels serve as a reference to determine the required level of treatment, and are standard among most testing laboratories. A class level of 0 is considered a negative reading, while level 1 means an equivocal or unclear reading. Class levels of 2 and 3 are deemed positive readings, but levels 4, 5 and 6 rank as strongly positive.
Different levels of IgE can assist in determining which allergen caused the allergic reaction. In the reference book "Mosby's Manual of Diagnostic and Laboratory Tests," registered nurse Kathleen D. Pagana and Dr. Timothy J. Pagana explain that a patient has been exposed to a particular allergen before skin testing, a blood test may provide more accurate results than a skin test.
Based upon the type of allergen, the accuracy rates for blood-based allergy tests range between 45 percent and 95 percent, according to the Paganas. Even if an individual tested more than once shows a continued higher level of a particular antibody, that does not necessarily indicate a high level of reaction to a specific allergen. In some cases, individuals known to have higher class levels of IgE in their system exhibit no symptoms at all when exposed to the allergen.
After the IgE class has been determined, class levels help the physician and patient choose appropriate treatment options. For instance, with an IgE level in the low range, the patient may be able to avoid certain allergens, such as cat dander. If the IgE level appears high, however, the necessary protocols for immunotherapy -- such as allergy shots -- may be required.