Objectives/hypothesis: Intradermal dilutional testing (IDT) has been considered more sensitive than prick testing for detecting low-level allergies. Multi-Test II is one of the most sensitive and reproducible prick testing methods available. This study compares Multi-Test II prick testing with IDT.
Design: Retrospective chart review and data analysis on patients who had allergy testing with both Multi-Test II and IDT.
Setting: Outpatient allergy clinic in the otolaryngology department of an academic tertiary care medical center.
Population: Forty adult patients had complete allergy testing with both Multi-Test II and IDT for a standard panel of twelve antigens between January 2002 and April 2002.
Intervention: Analysis and comparison of test results on Multi-Test II and IDT for each antigen separately and across all antigen tests together.
Results: Forty patients had complete testing for all antigens during the time period for the study. Six of these patients did not react to the positive control on Multi-Test II and were eliminated from the main analysis. Of the 34 patients included in the main analysis, all were positive for at least one antigen on IDT; one half (17/34) were negative for all antigens on Multi-Test II. A significantly greater number of patients were positive on IDT than Multi-Test II for all antigens except dog (P < 0.05). There was a statistically significant correlation between IDT endpoint and Multi-Test II score for several antigens (P < 0.05). Of 408 total antigen tests performed, 339 (83.1%) were negative on Multi-Test II. Of these 339 negative Multi-Test II tests, 148 (43.7%) were negative on IDT and 191 (56.3%) were positive on IDT; 174/339 (51.3%) had an IDT endpoint of 2 or 3 and 17/339 (5.0%) had an IDT endpoint > or = 4. A significantly greater number of antigen tests were positive on IDT than on Multi-Test II (P < 0.001). The overall Spearman correlation coefficient between IDT endpoint and Multi-Test II score was 0.370 (P < 0.001).
Conclusion: Patients were more likely to have a positive test on IDT than on Multi-Test II. IDT therefore may be a more sensitive testing technique for inhalant allergies than Multi-Test II prick testing. In addition, Multi-Test II score may not be a good predictor of IDT endpoint. Although a statistically significant correlation is demonstrated between Multi-Test II score and IDT endpoint, the correlation coefficient is low enough that clinical application may not always be safe or appropriate. The clinical significance of positive IDT results in the presence of negative Multi-Test II results is not known.