Diagnosis of occupational asthma from serial measurements of forced expiratory volume in 1 s (FEV₁) using the Area Between Curves (ABC) score from the Oasys plotter

Abstract

ObjectivesTo 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.MethodsThe 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).ResultsA 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.ConclusionsThe 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.

Pulmonary Function Testing in Work-Related Asthma: An Overview from Spirometry to Specific Inhalation Challenge

“…Based on serial PEF measurements, another diagnosis score for OA has also been proposed. Based on computed PEF analysis on days on and out of work, calculation from the area between the curves (ABC) of PEF allows the elaboration of a score (ABC score) that can be useful in the diagnosis of OA [33,34]. A score of 15 L/min/h between rest and workdays allows the highest specificity and a score of 5.6 L/min/h provides a good combination of reasonable sensitivity and specificity.…”

What good came out of the Covid-19 outbreak for workers with occupational asthma?

“…Peak Expiratory Flow (PEF) has advantages in the diagnosis of occupational asthma from the Oasys analysis of 2-hourly measurements over several weeks [14,15]. In this situation, PEF has been shown to be at least as sensitive and specific as FEV 1 [16], is cheaper, and the acquisition of reliable repeatable measurements easier than with unsupervised FEV 1 measurements. The analysis of serial 2-hourly PEF measurements is the method of choice for validation of the diagnosis of occupational asthma in those with a history of work-related symptoms [17].…”