SEASONAL-VARIATION IN IMMEDIATE SKIN-TEST REACTIONS

Seasonal variation in the size of immediate prick skin tests was exami ned in relation to changes in seasonal pollen exposure. Immediate skin test reactions to serial 5-fold dilutions of: (1) a specific pollen d uring its season (short ragweed), (2) a specific pollen from an earlie r season (tree), (3) a perennial allergen (D farinae, D pteronyssinus, or cat), and (4) histamine were examined at the projected trough of r agweed-specific IgE (2nd week in July), at the peak ragweed pollen cou nt (3rd week August), at the estimated peak in ragweed-specific IgE (4 th week in September) and at a time of no pollen exposure (2nd week in February). All 30 subjects had symptoms of rhinitis during the ragwee d season and a 3 mm or greater wheal to: 100,000 AU/mL of short ragwee d, 1:20 wt/vol of a tree exact, and a perennial allergen either 100,00 0 AU/mL of cat or 10,000 AU/mL of D farinae or D pteronyssinus. The me dian equivalent dose (dose of skin test material required to produce t he median skin test index score) for the four time periods revealed si gnificant seasonal differences. The reactions in October and February were significantly greater than those in July and August for all skin test agents. Histamine, ragweed, and trees showed maximal sensitivity in October, while perennial allergens demonstrated a peak in skin test sensitivity during mid-February.