Systemic reactions associated with subcutaneous allergen immunotherapy: timing and risk assessment

Background Subcutaneous allergen immunotherapy (SCIT) is associated with risk of systemic reaction. Although risk factors have been identified, the incidence of immunotherapy-related systemic reactions has not changed in recent years. Objectives To examine patterns of systemic reaction and determine whether risk of systemic reaction from SCIT is associated with patterns of response to skin tests to inhalant allergens recorded before receiving SCIT. Methods We carried out a retrospective review from January 2001 to December 2007. Patterns of systemic reaction from immunotherapy were examined. Cases were matched with controls by age (±10 years), sex, and time of injection (±1 week) to determine whether a pattern of more than 33% 3+ and 4+ skin test responses is associated with elevated risk for systemic reaction. Results Rate of systemic reaction from SCIT was 0.28% (46/16,375) per injection visit. Twenty patients had 46 systemic reactions. All severe reactions occurred within 30 minutes. The estimated odds of systemic reaction were almost 6 times higher for patients with more than 33% 3 to 4+ positive skin tests (OR = 5.83; 95%CI: 1.23–27.59, P = .026). For each additional 4+ skin test, the estimated odds for systemic reaction increased by 17% ( P = .020). Conclusions A small number of patients receiving SCIT account for a large proportion of systemic reactions. Skin test patterns demonstrating a greater number of larger skin tests responses to inhalant skin testing are associated with significantly elevated risk for systemic reaction in patients receiving SCIT.