A New Diagnostic Score for Occupational Asthma: The Area Between the Curves (ABC Score) of Peak Expiratory Flow on Days at and Away From Work

doi:10.1378/chest.08-0778

Chest

Volume 135, Issue 2, February 2009, Pages 307-314

https://doi.org/10.1378/chest.08-0778 Get rights and content

Background

Evidence-based guidelines recommend serial measurements of peak expiratory flow (PEF) on days at and away from work as the first step in the objective confirmation of occupational asthma. The aim of this study was to improve the diagnostic value of computer-based PEF analysis by using the program Oasys-2 to calculate a score from the area between the curves (ABC) of PEF on days at and away from work.

Methods

Mean 2-hourly PEFs were plotted separately for workdays and rest days for 109 workers with occupational asthma and 117 control asthmatics. A score based on the ABC was computed from records containing ≥ 4 day shifts, ≥ 4 rest days, and ≥ 6 readings per day. Patients were randomly classified into two data sets (analysis and test sets). Receiver operator characteristic (ROC) curve analysis determined a cutoff point from set 1 that best identified those with occupational asthma, which was then tested in set 2.

Results

Logistic regression analysis showed that all ABC PEF scores were significant predictors of occupational asthma, with the best being ABC per hour from waking (odds ratio, 11.9 per 10 L/h/min; 95% confidence interval, 10.8 to 13.1). ROC curve analysis showed that a difference of 15 L/min/h provided a high specificity without compromising sensitivity in diagnosing occupational asthma. Analysis of data set 2 confirmed a specificity of 100% and sensitivity of 72%.

Conclusion

The ABC PEF score is sensitive and specific for the diagnosis of occupational asthma and can be calculated from a shorter PEF surveillance than is needed for the current Oasys-2 work effect index.

Section snippets

Computing the ABC PEF Score by Time of Day

The average 2-h PEF plot is a graph in the Oasys program of the mean rest-day and workday PEF values plotted in 2-h segments according to the time of the day (in relation to the 24-h clock). It plots the mean of all workday readings taken between, for example, 6:30 am and 8:30 am as one data point, then all those taken between 8:30 am and 10:30 am as the next point, and so on in 2-h segments throughout the 24 h of the day. The rest day readings are then plotted in the same way in 2-h segments (

Results

After removal of patients who did not fulfill our inclusion criteria, data set 1 included records from 55 occupational asthma-positive patients and 59 occupational asthma-negative patients. Test set 2 contained records from 54 occupational asthma-positive patients and 58 occupational asthma-negative patients.

Table 1 shows the distribution of the three diagnostic tests that were used as the independent validators for occupational asthma in both data sets 1 and 2. The distribution of tests was

Discussion

This study has developed a new scoring system for occupational asthma based on serial PEF measurements analyzed by Oasys-2 software. using the average 2-h plot of PEF on days on and off work, by clock time, or time from waking up. We found that all scores investigated were significant predictors of occupational asthma. Furthermore, a score based on the area between rest-day and workday curves per hour from waking was the strongest predictor of occupational asthma and explained the largest

Conclusions

The ABC score is a new scoring system based on mean PEF on days on and off work for diagnosing occupational asthma from serial PEF recordings, which can be calculated from shorter records than needed for the current Oasys-2 scoring system. A score of 15 L/min/h between rest days and workdays provides the highest specificity without compromising sensitivity, and 5.6 L/min/h provides an optimal combination of reasonable sensitivity and specificity based on ROC analysis. Even at 10 L/min/h,

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: This project was funded by a PhD fellowship from the COLT Foundation.

: Drs. Burge, Vellore, and Robertson have no conflicts of interest to disclose. Dr. Jaakkola has received some travel awards for scientific meetings from GlaxoSmithKline and MSD. Mrs. Moore received COLT fellowship funds for her part-time PhD, of which this research forms a part. The work is presented at international and national meetings and spoken about in smaller groups as part of teaching about the diagnosis of occupational asthma.

: Reproduction of this article is prohibited without written permission from the American College of Chest Physicians (www.chestjournal.org/misc/reprints.shtml).

¹: Dr. Burge promotes and disseminates the use of serial measurements of peak expiratory flow for the diagnosis of occupational asthma. His department receives some monies from grants, donations, and legal fees to support the research. He has no personal financial interest. Dr. Pantin has published on the subject of OASYS software to enhance its reputation, and otherwise has no conflict of interest relating to this article.

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Chest

Original ResearchAsthmaA New Diagnostic Score for Occupational Asthma: The Area Between the Curves (ABC Score) of Peak Expiratory Flow on Days at and Away From Work

Background

Methods

Results

Conclusion

Section snippets

Computing the ABC PEF Score by Time of Day

Results

Discussion

Conclusions

Am J Respir Crit Care Med

J Allergy Clin Immunol

Am J Med

Chest

J Allergy Clin Immunol

J Allergy Clin Immunol

SWORD ‘99: surveillance of work-related and occupational respiratory disease in the UK

Occup Med

Evidence based guidelines for the prevention, identification, and management of occupational asthma

Occup Environ Med

Health, employment and financial outcomes in workers with occupational asthma

Br J Ind Med

Non-specific hyperreactivity in workers exposed to toluene diisocyanate, diphenyl methane diisocyanate and colophony

Eur J Respir Dis

Clinical and socio-professional fate of isocyanate-induced asthma

Clin Allergy

Original Research
Asthma
A New Diagnostic Score for Occupational Asthma: The Area Between the Curves (ABC Score) of Peak Expiratory Flow on Days at and Away From Work