degree of sensitization of the cutaneous mast cells and their ability to release histamine, and the reactivity of the skin to the mediators released (H. S. Nelson, 1983). The advantages of skin testing are its simplicity, rapidity of results, low cost, and high sensitivity; however, skin tests can be subject to abuse through inappropriate use or overuse. Table 5-4 presents a comparison of some in vivo and in vitro methods for the diagnosis of IgE-mediated allergic disease.

Major Methods

Two major skin testing methods are commonly used: the skin prick or puncture test and the intradermal test. In the prick method, a drop of allergenic extract is applied to the skin, and the skin is pricked with a needle through the drop. A number of devices are commercially available for testing using this method (Demoly et al., 1991). The most commonly used skin prick method is to introduce the tip of a stylette or a 27 (or smaller) gauge needle into the epidermis at a 15- to 20-degree angle through the drop of test allergen and then to lift up until the tip of the needle pops loose. Alternatively, lancets or solid needles are often used.

One concern about the skin prick method is the possible transfer of allergens from one test site to another if the needle is not properly wiped off

TABLE 5-4 Comparison of Two In Vivo Skin Tests (Prick and Intradermal) with In Vitro Tests (RAST or Equivalent) for Diagnosing IgE-Mediated Allergic Diseasea

 

In Vivo Skin Tests

 

In Vitro (Specific IgE)— RAST or Equivalent

Parameter

Skin Prick

Intradermal

Sensitivity

Good

Excellent

Fair-good

Specificity

Good

Poor-fair

Excellent

Safety

Excellent

Good

Excellent

Reproducibility

Good

Good

Excellent

Convenienceb

Excellent

Good

Fair

Cost

Excellent

Good

Fair

NOTE: RAST, radioallergosorbent test.

a Ratings are based on the assumption that the procedures are done by well-qualified personnel using properly standardized reagents and adequate quality control.

b Convenience is a composite of efficiency and ease of testing, lack of discomfort, and rapid availability of test results.

SOURCE: Adapted from Van Arsdel and Larson, 1989.



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