SELECTED ARTICLES FROM THE RECENT LITERATURE 2004

12/16/04

Relationship between skin test and bronchial reactivity to allergens

Summary
Background - It is well established that a definite positive skin test (ST) to aeroallergens such as pollens is predictive of a positive bronchoconstrictive response when the allergen is inhaled by the same subject. However, the quantitative aspects of this relationship are more complex, likely also involving the degree of non-specific bronchospastic reactivity of the subject to inhaled agents such as histamine or methacholine.

Findings - Cockcroft et al of the Univ of Saskatchewan in Canada examined 156 allergen challenges for the relationship between: 1) the dose of allergen causing a 20% decrease in FEV-1 (Allergen PC 20); 2) minimum concentrations of allergen inducing a positive prick ST response (ST-min); 3) the degree of non-specific airways reactivity as assessed by the concentration of methacholine needed to induce a 20% decrease in FEV-1 (Meth-PC20).

They found, using single regression analyses, a significant correlation between the allergen PC20 and both the allergen conc in the ST-min and the Meth-PC20 (p=0.0015 to p<0.00005). Using multiple regression analyses, even closer correlations were seen so that the Allergen PC20 could be predicted for an individual patient within 3 doubling concentrations in over 90% of the cases.

Reference
Allergy 2005;60:56-60

Editor's Comments
I have reviewed this laboratory research-type report because of the clinical relevance involved. It has been long known that being very reactive to low concentrations of allergen in skin testing is a risk factor for exhibiting an asthmatic reaction when inhaling the allergen. However, many very aeroallergen sensitive individuals never develop asthma reactions when exposed to high ambient concentrations of that allergen even though they may exhibit severe allergic rhinitis responses.

These findings confirm and extend earlier studies showing that the degree of non-specific bronchial hyper-reactivity plays a key role in determining whether an asthmatic reaction occurs when the allergen is inhaled, - at least in a solution form. There is still some question whether inhalation challenge with aeroallergen solutions replicates the "natural" exposure to particular pollen material in our environment.

 

 

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