Usefulness of Repeated Measurements of Bronchial Hyperresponsiveness for the Diagnosis of Occupational Asthma

Abstract

To assess the usefulness of repeated measurements of nonspecific bronchial hyperresponsiveness (BHR) in the diagnosis of occupational asthma, we studied 26 consecutive patients referred to the Clinic of Occupational Medicine in Copenhagen because of suspected occupational asthma. The diagnosis of bronchial asthma was confirmed in all patients; however, 4 patients were excluded from the study as they had a baseline PC₂₀ FEV₁, histamine > 8 mg/ml. A bronchial challenge test with histamine was performed after nonspecific exposure at the workplace and after a specific bron-choprovocation test in the laboratory; substantial increase in BHR (BHR_work and BHR_lab, respectively) was defined as a change in PC₂₀ of at least one doubling concentration. A fall in FEV, of at least 20% from baseline after the specific bronchoprovocation test was defined as a positive response (SBP_pos). Six patients had BHR_work and 7 patients had BHR_lab; 2 patients had both BHR_work and BHR_lab. Five patients had SBP_pos, of whom 1 had BHR_work and 1 had BHR-_lab. None of the patients had three positive tests, i.e., BHR_work, BHR_lab, and SBP_pos. In 3 patients the specific challenge test caused a pronounced decline of lung function and deterioration in the clinical condition. With the results of the specific challenge test as the gold standard, serial measurement of his-tamine responsiveness may not appear to be a sensitive diagnostic test for occupational asthma. However, the high number of patients with an increase in BHR after specific and/or nonspecific occupational exposure strongly suggests that changes in bronchial responsiveness may identify patients with respiratory symptoms causally related to occupational exposure. Further studies are needed to ascertain whether repeated measurements of nonspecific bronchial responsiveness performed at work and in the laboratory can in some cases replace the time-consuming and potential hazardous specific bronchial provocation tests.