Abstract

Background:
Existing analyses to identify work-related asthma (WRA) using serial peak expiratory flow (PEF) include the area between the curve (ABC) score that characterizes the difference between summary curves of hourly PEF on rest days and work days. The cutoff value for WRA using the PEF-ABC score is 15 liters/minute/hour (l/min/hr). Many portable devices that measure serial PEF also concurrently measure and record the forced expiratory volume in one second (FEV1). Serial FEV1 might facilitate the identification of WRA cases, although currently there are no validated criteria to judge work-related status using this metric. We used serial spirometry data from adults with asthma to examine whether ABC scores based on FEV1 (FEV1-ABC) might identify the same or different WRA cases as those implicated by
PEF-ABC scores.

Methods:
The study sample comprised 95 working adults with asthma who were enrolled in a health maintenance organization in the US state of Massachusetts and participated in a study of asthma. Each participant completed at least two weeks of self-testing using a portable spirometer that recorded and time/date stamped PEF and FEV1. We calculated PEF-ABC scores and applied the existing cutoff point of 15 l/min/hour for a positive work-related status, which was fulfilled by 7 participants. Without validated criteria to interpret FEV1-ABC scores, we compared the participants with the 7 highest FEV1-ABC scores (>=0.06 l/hour) to the group of 7 with PEF-ABC scores >=15.

Results:
The 95 asthma cases were 71% female with a mean age of 34 years, and worked predominantly in management, professional, and business (48%) and sales and office (28%) occupations. Their PEF-ABC values ranged from -50 to +50 with median=-1.97, and FEV1-ABC values ranged from -0.33 to +0.26 with median=-0.04. The two groups (n=7 in each) with high ABC scores shared 4 participants in common. The three cases with evidence for WRA based only on an elevated PEF-ABC score were in the 9th (n=1) and 8th (n=2) deciles of
FEV1-ABC scores. The three cases with evidence for WRA based only on an elevated FEV1-ABC score were in the 10th, 8th, and 3rd deciles of PEF-ABC scores.

Conclusion:
Serial FEV1 might help to identify WRA cases when used in conjunction with serial PEF. However, further work is needed to establish and validate criteria for WRA using serial FEV1.

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