Original article
Sensitivity and specificity of PC20 and peak expiratory flow rate in cedar asthma

https://doi.org/10.1016/0091-6749(90)90098-OGet rights and content

Abstract

The diagnosis of red cedar asthma is usually confirmed by a specific challenge with plicatic acid, the compound responsible for the disease. We performed this study to determine the sensitivity and specificity of two other diagnostic tests, prolonged recording of peak expiratory flow rate (PEFR) and measurement of bronchial responsiveness (provocative dose of methacholine causing a 20% fall in FEV1 [PC20 methacholine]). Twenty-three patients with suspected cedar asthma participated in the study. The patients recorded PEFR during 2 weeks away from work and 3 weeks at work. PC20 was measured both at the end of the nonworking and working period. An obvious decrease in PEFR in 2 of 3 working weeks, when PEFRs of weekends or holidays were compared (by visual inspection of the PEFR recording), and a decrease in PC20 by more than a twofold dilution, when the patient returned to work, were considered as positive tests for cedar asthma. Plicatic acid challenge test was performed at the end of the study; 14 patients reacted, whereas nine patients did not. With the results of the plicatic acid challenge test as the gold standard, the sensitivity and specificity of PEFR recordings were 86% and 89%; changes in PC20, 62% and 78%; and 93% and 45% for a positive clinical history. The combination of PEFR and clinical history revealed a 100% sensitivity with a 45% specificity. Combination of PEFR and PC20 did not improve the diagnostic accuracy. We conclude (1) that the specific challenge with plicatic acid is not necessary when both clinical history and PEFR are negative, (2) that, if either the history or PEFR is positive for occupational asthma, the plicatic acid test must be done to rule out false positive cases, and (3) serial measurement of PC20 methacholine is not a valuable test in cedar asthma.

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Cited by (115)

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    Another approach is by monitoring patients' peak expiratory flow for two weeks while patients are at work, and another for two weeks while patients are away from work [19]. Although a good association has been found between peak expiratory flow monitoring and specific challenge tests, this diagnostic approach has been criticised because it depends heavily on patients’ cooperation, reliable performance, and recording correct readings [20,21]. The ideal treatment for occupational asthma patients with a latency period is the removal from exposure.

  • Assessment and Management of Occupational Asthma

    2020, Journal of Allergy and Clinical Immunology: In Practice
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Supported by the Workers' Compensation Board of British Columbia.

Johanne Côté, MD, is a recipient of a scholarship from the Canadian Lung Association and the Quebec Health Research Foundation.

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