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Wise et al.

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rare reports of anaphylaxis and no reported fatalities. 818 SPT can be performed in any age group and is of particular value in pediatric populations given the speed at which multiple antigens can be applied and the limited discomfort experienced during testing. Skin testing is not appropriate in all patients. Absolute or relative contraindications to SPT include uncontrolled or severe asthma, severe or unstable cardiovascular disease, concurrent beta-blocker therapy, and pregnancy. Certain medications and skin conditions may interfere with skin testing. These are covered in detail in section VIII.E.4. Issues that affect the performance or interpretation of skin tests: VIII.E.4.a. Medications; and VIII.E.4.b. Skin conditions, respectively. Aside from an excellent safety profile, SPT has a reported sensitivity and specificity around 80%. 818-820 It is reported to be more sensitive than serum testing with the added benefit of lower cost. 818,821,822 Despite studies aimed at comparing SPT, intradermal testing, and serum testing, conclusive evidence that one type of testing is superior to the others is lacking. 761 The number and choice of antigens used in testing varies considerably between clinical practices. A panel of antigens representing an appropriate geographical profile of allergens that a patient would routinely be exposed to is recommended. Positive (histamine) and negative (glycerin or saline) controls should always be included. Variability in quality and potency between commercially available allergen extracts has been demonstrated. 823,824 Therefore, whenever possible, standardized allergens should be used. 820 SPT is performed with lancets, which come in a variety of forms. Generally, lancets are designed to limit skin penetration depth to 1 mm. However, varying amounts of pressure applied to the delivery device can alter the depth of skin penetration, which ultimately influences the skin reaction to an antigen. 825 Prick testing devices can come as single-lancet devices or multiple-lancet devices. Multiple-lancet devices have the advantage of being able to rapidly apply multiple antigens to the skin at 1 time with a more consistent amount of pressure. 826,827 Wheal size, sensitivity, and reproducibility all differ from 1 device to another 826-828 ; therefore, any healthcare provider performing SPT must thoroughly familiarize themselves with his/her testing device. Typically, the lancet is dipped into a well containing an antigen and then applied to the skin. The volar surfaces of the forearms and the back are the most common testing sites for SPT. Choice of site is directed by the age/size of the patient. Tests should be applied 2 cm or greater apart as placing them closer to one another can cause cross-contamination. 829 After 15 to 20 minutes, the results are read by measuring the size of the wheal by its greatest diameter. A wheal 3 mm or larger than the negative control is considered positive. There is a large body of evidence detailing the use of SPT in clinical practice (Table VIII.E.1). Based upon several prospective studies and systematic reviews, SPT has been demonstrated to be a safe method of allergy testing. It is not inferior to serum or intradermal testing and is less expensive than serum testing. It does carry a risk of systemic reaction, so caution should always be exercised. It is also associated with some discomfort during testing; however, the discomfort is generally less than that experienced during intradermal

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Int Forum Allergy Rhinol . Author manuscript; available in PMC 2020 June 10.