Associations between case history and the results of bronchial methacholine challenge testing (BMT) and specific bronchial challenge with the suspected allergen (specific challenge testing) in patients with suspected occupational asthma (OA) were examined. A group of 229 patients with presumed OA were evaluated at an occupational health clinic between 1992 and 1995. Sixty two were health care workers who had had contact with latex gloves, 28 were bakers, 114 were isocyanate workers, and 25 were hairdressers. Following BMT of the subjects, the results were compared with those obtained in a previous study with 81 healthy volunteers. The patients underwent specific challenge testing. All patients except the hairdressers completed a respiratory symptom questionnaire and were interviewed by an experienced physician concerning symptoms and work history. The median age of the health care workers, bakers, and hairdressers was around 30 years (yr), of the isocyanate workers about 40yr. Approximately 48 to 61% of the subjects in the different occupational groups responded positively to BMT. Only 12 to 25% of the subjects demonstrated a significant bronchoconstrictive reaction to specific challenge testing. A positive BMT result was significantly associated with a specific challenge testing result only in the health care workers with suspected latex allergy. Approximately 40 to 72% of the patients in the different occupational groups had a positive OA case history. Positive case histories were significantly associated with a positive specific challenge testing result only in the bakers and isocyanate workers. OA positive case histories in the health care workers were frequently associated with negative specific challenge testing results. Positive BMT results were strongly associated with OA positive case histories in the isocyanate workers, but not in the other groups. When positive BMT results and OA positive case histories were combined, they had a specificity for diagnosing OA, using the result of specific challenge testing as the gold standard, of 62 to 86%. The sensitivity was lower, 52 to 83%. The authors conclude that the combination of BMT results and case history is a reasonable screening tool for diagnosing OA. The gold standard for diagnosing OA, however, is still specific challenge testing in conjunction with a corresponding case history.

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