Table 2 Variables that can affect SPT results

Controllable

• Patient Variables

• Choosing the appropriate anatomic site for testing [26–29]

• Distance between SPT sites [26, 27]

• Proximity of control tests to the allergen tests [23]

• Documentation of any unusual skin trauma [16]

• Performance Variables

• Consistent technique used for administering controls and allergen extracts [23] (e.g., uniformity in the depth of penetration)

Control may depend on who is able to influence certain factors in the clinical/research environment

• Patient Variables

• Awareness of the attenuating/confounding effects of medication [13, 22]

• Test Supply Variables

• Quality/potency of test allergy extract [22]

• Source of the extracts [15]

• Variables in Reading the Test

• Choice of a qualitative, semi-quantitative, or quantitative method for reporting cutaneous reactivity to allergens

Uncontrollable

• Patient Variables

• Age of patient/subject [30, 31, 24]

• Racial factors (i.e., skin color) [8]

• Sun damage of skin [13]

• Existing disease processes, (e.g., hypertension, diabetes, immunodeficiency that may interfere with the development of a skin test reaction) [23]