Inhalation challenges with occupational agents: threshold duration of exposure.

Objectives: The aim of this study was to characterize the threshold duration of exposure needed to elicit an asthmatic reaction during specific inhalation challenges (SIC) with various occupational agents and to determine the duration of exposure that should be completed before the test can be considered negative.

Methods: This retrospective study analysed the cumulative duration of challenge exposure that was required to elicit a ≥20% fall in forced expiratory volume in one second in 335 consecutive subjects with a positive SIC.

Results: The threshold duration of challenge exposure required to induce an asthmatic reaction was ≤60 min in 179 (53%) subjects, between 61 and 120 min in 74 (22%) subjects, and longer than 120 min in 82 (25%) subjects. The multivariate linear regression analysis showed that a longer duration of exposure was associated with exposure to low-molecular-weight agents (p < 0.001), a higher level of baseline non-specific bronchial hyperresponsiveness to histamine (p = 0.015), increasing age (p = 0.011), and a shorter duration of asthma symptoms at work (p = 0.060).

Conclusions: This study demonstrates that the sensitivity of SICs for diagnosing OA is highly dependent upon the duration of the challenge exposure. These data may provide useful guidance for improving the reliability of SICs performed with realistic methods of exposure.