Assessing the value of skin prick tests

Abstract

Skin test materials vary in their potency and specificity. Although 3 mm reactions are often regarded as diagnostic of a type 1 allergy, a study based on 100 alergy clinic patients with food intolerance showed that 13 out of 15 patients with a 3 mm reaction to common inhalant allergens had no RAST[radioallergosorbent test]-detectable allergen-specific Ig[immunoglobulin]E. Three millimeter reactions were significant for milk and egg extracts. Food intolerance was clinically demonstrable in 6 out of 7 patients giving a 4 mm skin reaction and in 10 out of 13 with a 3 mm reaction. There was, a clinically false positive reaction of 3 mm or more in 3.8% of allergy clinic patients for milk and 2.8% for egg. In 15 out of 19 patients with a clinical diagnosis of fish allergy, the diagnosis was supported by a skin test reaction of 5 mm or more. Seven patients with no history of intolerance to fish gave a 4 mm reaction to the same extract. Reactions of less than 5 mm were thus unhelpful clinically.