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Table 2 Variables that can affect SPT results

From: Skin prick/puncture testing in North America: a call for standards and consistency

Degree of Control Possible Source of Variability Variable
Controllable • Patient Variables • Choosing the appropriate anatomic site for testing [2629]
• 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]