Immunotherapy decreases skin sensitivity to ragweed extract: demonstration by midpoint skin test titration

New approaches to allergen immunotherapy

Allergic diseases are common problems affecting 20% to 30% of the US population. Mast cells and basophils are the primary effector cells mediating allergic inflammation through the triggering of membrane immunoglobulin E receptors (FceRI) with antigen. Allergen immunotherapy is used as one treatment for allergic disease and results in the inhibition of mast cell and basophil responses through unknown mechanisms. In this review, we examine potential mechanisms that could result in blunted human mast cell/basophil functional responses, strategies aimed at using these mechanisms to develop new immunologically based therapies, and recent findings that have broad implications toward our understanding of how mast cells/basophils become desensitized.

Optimal skin prick wheal size for diagnosis of cat allergy

BACKGROUND

The skin prick test is the diagnostic procedure of choice for determination of immediate hypersensitivity. A wheal diameter of 3 mm or larger is generally accepted as the cutoff for a positive test result, although the validity of this assumption has not been rigorously demonstrated.

OBJECTIVE

To determine the skin prick wheal size that best identifies clinical allergy to cat.

METHODS

Forty-five patients referred for evaluation of rhinoconjunctivitis underwent determination of atopic status by skin testing using the Greer Dermapik device and a combination of other modalities, including history, in vitro determination of specific IgE level, and nasal challenge with standardized cat pelt extract. Parameters evaluated before and after nasal challenge included symptom score and nasal lavage tryptase and prostaglandin D (PGD2) levels.

RESULTS

The widely accepted 3-mm wheal for a positive skin test result to cat is highly sensitive but only moderately specific for diagnosis of cat allergy as evaluated by history, specific IgE level, postchallenge symptom score, and tryptase and PGD2 levels. Optimal cutoffs for a positive skin test result to cat based on receiver operating characteristic analysis and 95% positive predictive value were 5.5 mm or greater for each of these parameters. When a true-positive result for cat allergy was defined as a combination of positive history, specific IgE level, postchallenge symptom score, and tryptase and PGD2 levels and a true-negative result as all of these parameters being negative, a 6-mm cutoff was able to distinguish cat allergic from cat nonallergic individuals.

CONCLUSION

In a potentially allergic population undergoing skin prick testing with the Greer Dermapik using standardized extracts, a 3-mm skin prick wheal will overestimate the presence of cat allergy. A 6-mm wheal appears to distinguish those individuals who are cat allergic from those who are not.

The ACVD task force on canine atopic dermatitis (XVII): intradermal testing

Intradermal testing has been practiced for decades in human and veterinary medicine. The primary utility of intradermal testing is in the demonstration of IgE-mediated allergen hypersensitivity. The presence of a positive reaction on an intradermal test is not always indicative of allergy, as it may sometimes be an indication of sub-clinical hypersensitivity. Despite its widespread use by veterinary dermatologists, the usefulness of the intradermal test would be greatly enhanced by the use of standardized allergen extracts and homogeneous criteria for the interpretation of results. Irrespective of these shortcomings, intradermal testing is regarded as a valuable tool in the demonstration of allergen-specific hypersensitivity when performed according to accepted guidelines.