Background: The relationships between allergic symptoms after exposure to house dust, allergy parameters (skin test to house dust mite [HDM], total IgE, HDM-specific IgE, and blood eosinophil counts), and several confounding variables (age, sex, smoking habits, and airway hyperresponsiveness) were evaluated in 235 patients with asthma and chronic obstructive pulmonary disease (COPD).
Results: Skin tests had higher diagnostic value (sensitivity plus specificity) for symptomatic allergy than specific IgE (1.45 versus 1.36) or total IgE (1.16). The other allergy parameters gave no additional information on symptoms once the skin test was known. Expressing the skin test relative to the histamine control proved slightly better than uncorrected wheal size, but this probably has limited clinical value. The best cutoff level for a positive skin test was 0.7 when the histamine wheal size was accounted for by division, -6 mm when subtraction was used, and 7 mm for absolute wheal size. These cutoff levels proved equally applicable in various subgroups of patients with asthma and COPD. Only the skin test and female sex were independent predictors of allergic symptoms.
Conclusion: We conclude that skin tests to HDM are better predictors for clinical allergy than total or specific IgE levels and eosinophil count, and that they are applicable in most patients with asthma and with COPD.