Comparison of the intradermal irritant threshold concentrations of nine allergens from two different manufacturers in clinically nonallergic dogs in the USA.

Background: The intradermal irritant threshold concentration for many allergens is unknown.

Objective: To determine the intradermal irritant threshold concentration (ITC) of nine allergens from two different manufacturers.

Animals: Twenty privately owned clinically nonallergic dogs.

Methods: Alternaria, cat dander, Dermatophagoides farinae, Chenopodium album (lamb's quarter), Xanthium strumarium (cocklebur), Prosopis glandulosa (mesquite), Morus alba (white mulberry), Cynodon dactylon (Bermuda grass) and Phleum pretense (Timothy grass) from two manufacturers (ALK; Round Rock, TX, USA and Greer Laboratories; Lenoir, NC, USA) were injected intradermally at two dilutions and at 15 and 30 min evaluated subjectively (1-4) and objectively (horizontal wheal diameter) by two blinded investigators. A subjective score of 3 or 4 by either investigator at either timed reading was considered positive. If both concentrations resulted in positive reactions, two additional dilutions were performed. The ITC was defined as the lowest tested concentration that elicited a positive reaction in ≥10% of animals.

Results: The ITCs were Alternaria >2,000 PNU/mL; cat dander 750 PNU/mL (ALK) and 2,000 PNU/mL (Greer ); D. farinae <1:10,000 w/v; C. album <6,000 PNU/mL; X. strumarium <6,000 PNU/mL; P. glandulosa <500 PNU/mL; M. alba <6,000 PNU/mL; C. dactylon <10,000 PNU/mL (ALK) and <6,000 PNU/mL (Greer ); and P. pretense <6,000 PNU/mL.

Conclusions And Clinical Significance: There were significant differences in subjective scoring and objective measurement between manufacturers for Alternaria, cat dander and P. pretense. Results revealed significant positive correlation between subjective scoring and objective measurement for each time, investigator and manufacturer separately.