Abstract

Objectives
To identify the changes in serial 2-hourly forced expiratory volume in 1 s (FEV1) measurements required to identify occupational asthma (OA) using the Oasys Area Between Curves (ABC) score.

Methods
The ABC score from 2-hourly measurements of FEV1 was compared between workers with confirmed OA and asthmatics without occupational exposure to identify the optimum separation using receiver operator characteristic (ROC) analysis. Separate analyses were made for plots using clock time and time from waking to allow for use in shift workers. Minimum record criteria were =6 readings per day, >4?day shifts and >4?rest days (or >9 days for controls).

Results
A retrospective analysis identified 22 workers with OA and 30 control asthmatics whose records reached the quality standards. Median FEV1 diurnal variation was 20.3% (IQR 16.1–32.6) for OA and 19.5% (IQR 14.5–26.1) for asthmatic controls. ROC curve analysis identified that a difference of 0.056?L/hour gave a ROC score of 0.821 for clock time and 0.768 for time from waking with a sensitivity of 73% and a specificity of 93% for the diagnosis of OA.

Conclusions
The diagnosis of OA requires objective confirmation. Unsupervised serial FEV1 measurements are more difficult to obtain reliably than measurements of peak expiratory flow, which are likely to remain the standard for general use. A FEV1 ABC score >0.056?L/hour provides a valid cut-off for those who wish to use FEV1 rather than peak expiratory flow.

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Comments

This paper extends the Area Between Curve analysis of serial lung function measurements in the diagnosis of occupational asthma from PEF to FEV1, and establishes the difference required to make a secure diagnosis of occupational effect at 0.056 litres/hour. Some favour FEV1 measurements to comply with quality requirements for spirometry, however they are more difficult to obtain and do not provide better quality diagnoses than the measurement of PEF.

10/27/2020