Accuracy of Two Cat Allergen Extracts in Predicting the Specific Bronchial Provocation Test Results

Article Outline

• Rationale
• Methods
• Results
• Conclusions
• Copyright

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Rationale 

It would be very useful to assess which concentration of Fel d 1 in allergen extracts used in skin prick testing (SPT) predicts the outcome of specific bronchial provocation test (BPT) more accurately.

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Methods 

Thirty-nine asthmatic patients (mean age 31.2 ± 8.4 years, female/male ratio 2.0) with positive results for SPT and/or detectable cat allergen serum specific IgE (CAP-System FEIA) underwent a BPT with cat epithelium. In addition, SPT with two allergenic extracts (cat dander 10 HEP/ml and 60 mcg/ml of Fel d 1 and cat dander 100 BU/ml and 40 mcg/ml of Fel d 1) were performed. Statistical analysis of results was carried out by Receiver Operating Characteristics (ROC) curves. Sensitivity, specificity, positive (PPV) and negative (NPV) predictive values for several cut-off points were also calculated.

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Results 

Cat epithelium BPT was positive in 24 subjects (61.5%). The area under the ROC curve for SPT-10 HEP/ml and SPT-100 BU/ml was 0.77 and 0.69 respectively. A 3 mm-SPT-10 HEP/ml papule had 100% sensitivity, 26% specificity, 68% PPV and 100% NPV. A 9 mm papule had 20% sensitivity, 93% specificity, 83% PPV and 42% NPV. A 3 mm-SPT-100 BU/ml papule had 96% sensitivity, 20% specificity, 65% PPV and 75% NPV. A 9 mm papule had 12% sensitivity, 86% specificity, 60% PPV and 38% NPV.

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Conclusions 

The power of skin tests to predict the BPT results with cat allergens is low or moderate. Accuracy improves when Fel d 1 allergen extract concentration increases.