Evaluation of three different histamine concentrations in intradermal testing of normal cats and attempted determination of ‘irritant’ threshold concentrations for 48 allergens

Abstract

The purpose of this study was to determine the optimal histamine concentration and 'irritant' allergen threshold concentrations in intradermal testing (IDT) in normal cats. Thirty healthy cats were tested with three different histamine concentrations and four different concentrations of each allergen. The optimal histamine concentration was determined to be 1: 50,000 w/v (0.05 mg mL(-1)). Using this histamine concentration, the 'irritant' threshold concentration for most allergens was above the highest concentrations tested (4,000 PNU mL(-1) for 41 allergens and 700 PNU mL(-1) for human dander). The 'irritant' threshold concentration for flea antigen was determined to be 1:750 w/v. More than 10% of the tested cats showed positive reactions to Dermatophagoides farinae, Dermatophagoides pteronyssinus, housefly, mosquito and moth at every allergen concentration, which suggests that the 'irritant' threshold concentration for these allergens is below 1,000 PNU mL(-1), the lowest allergen concentration tested. Our results confirm previous studies in indicating that allergen and histamine concentrations used in feline IDT may need to be revised.

Feline atopic dermatitis: a retrospective study of 45 cases (2001–2012)

“…Only limited evaluation of feline AD patients meeting strict diagnostic criteria, not reliant on allergen testing results, has so far been reported to assess potential feline AD subsets. There are suggestions that most cats with AD have weak reactions on IDT that make evaluation difficult, although in contrast, there are also reports of false positives in normal cats . In the present study, 68% of cats with confirmed AD that underwent allergen testing ( n = 19) had strong positive reactions on IDT.…”

“…Pollen and insect allergens were the most prevalent strong reactions, in contrast to previous studies on feline AD, in which house dust mites were more frequently implicated . Of note, irritant threshold concentrations for insect allergens, including flea, housefly, mosquito and moth, have recently been re‐evaluated for IDT in cats, and current recommendations are for lower testing concentrations than those used during the study period . However, less than one‐third of the cats had strong positive reactions to flea allergen on IDT in this cohort despite the study occurring in a flea endemic region.…”

Pilot study: prevalence of positive aeroallergen reactions in 10 cats with small‐airway disease without concurrent skin disease

“…It was interesting to note that more positive allergen reactions to house dust mites ( D. farinae and D. pteronyssinus ) were found with IDT, but not with IgE testing in affected cats (13/20) than in unaffected cats (4/20). It was recently reported that the irritancy thresholds for IDT allergens in cats may need to be changed and that many ‘positive allergen reactions’ may in fact be due to irritant reactions 18 . However, in another study, no evidence of irritancy was found 19 .…”

Determination of threshold concentrations of plant pollens in intradermal testing using fluorescein in clinically healthy nonallergic cats

“…Test reactions in cats are often subtle and can be more difficult to interpret than the skin reactions in dogs. Challenges with the IDT of cats arise because of poor and inconsistent wheal formation, an inability to assess test reactions due to rapid disappearance of the injected allergen solution, the use of nonstandardized concentrations of allergens and the influence of patient stress …”

“…The concentration of allergens used for IDT of dogs and cats is a subject of controversy in veterinary dermatology . Current recommendations for test concentrations of plant pollen allergens range from 1000 protein nitrogen units (PNU)/mL) to 8000 PNU/mL for dogs and there are no specific recommendations published for cats .…”