Comparative effectiveness of allergy testing method in driving immunotherapy outcomes

Background: Skin-prick testing (SPT), in vitro testing (IVT), and intradermal-dilutional testing (IDT) are methods to detect patient sensitivities to specific allergens and direct immunotherapy dosing. We used objective and subjective measures of improvement to compare outcomes based on test method.

Methods: Patients underwent 1 of 3 protocols: SPT, screening SPT followed by IDT, or IVT. We used institution billing data to do a cost analysis of these tests. The time to maintenance (TTM) therapy was analyzed and patients were stratified into high and low reactors. The Rhinoconjunctivitis Quality of Life Questionnaire (RQLQ) was used to quantify symptoms pre-maintenance and post-maintenance.

Results: Of 177 patients (SPT, n = 40; IVT, n = 91; IDT, n = 46), 115 (SPT, n = 35; IVT, n = 39; IDT, n = 41) were high reactors. Out of 90 patients (SPT, n = 17; IVT, n = 37; IDT, n = 36) reaching maintenance, 58 were high reactors (SPT, n = 15; IVT, n = 12; IDT, n = 31). Overall, SPT, IVT, and IDT median TTM were 542, 329, and 578.5 days, respectively. IDT TTM was shorter compared to IVT overall and in high reactors (hazard ratio [HR] = 1.91, p = 0.02; HR = 2.12, p = 0.03), but was not significant compared to SPT high reactors (p = 0.33). The IDT cost was $62.66, translating to an incremental cost-effectiveness ratio of $0.23 per day of shortened TTM. Median RQLQ change for the SPT, IVT, and IDT groups was 6.5, 1, and 1.5, respectively, but was not significant (p = 0.60).

Conclusion: IDT reached maintenance immunotherapy quicker than IVT but there was no difference compared to SPT. TTM did not correlate with improvements in patient symptoms between testing methods. This study represents a novel comparison of outcomes based on initial allergy testing method.