From the Guidelines
Yes, measurements of peak expiratory flow rates (PEF) at work and away from home are helpful in the diagnostic evaluation of occupational asthma.
Diagnostic Evaluation of Occupational Asthma
Serial PEF monitoring, performed multiple times daily both during work periods and when away from work (such as weekends and vacations), can reveal patterns of airflow limitation that correlate with workplace exposure.
- Patients should use a portable peak flow meter to record measurements at least four times daily for at least two weeks at work and two weeks away from work.
- The pattern typically shows decreased PEF values during work periods with improvement during time away from work.
- For reliable results, patients should be instructed to perform three measurements each time and record the highest value, along with noting the time, location, and any symptoms experienced. This monitoring approach is valuable because it provides objective evidence of the work-relatedness of symptoms, though it requires patient compliance and proper technique.
Combining Diagnostic Methods
The sensitivity and specificity of PEF monitoring improve when combined with other diagnostic methods such as specific inhalation challenges or immunological testing, as noted in studies such as 1 and 1.
- PEF monitoring is particularly useful when more specialized testing is unavailable or as an initial screening tool before proceeding to more definitive diagnostic procedures.
- According to 1, serial measurement of PEF on days at and away from work is the best validated method and is recommended in all guidelines.
Clinical Application
In clinical practice, the use of PEF monitoring in the diagnostic evaluation of occupational asthma is supported by guidelines such as those outlined in 1 and 1, which emphasize the importance of objective physiological tests and immunological tests in confirming occupational asthma.
- The management of work-related asthma guidelines, as discussed in 1, also highlight the role of PEF monitoring in the diagnostic process.
- Overall, PEF monitoring at work and away from home is a helpful tool in the diagnostic evaluation of occupational asthma, providing valuable insights into the relationship between workplace exposure and respiratory symptoms.
From the Research
Measurements of Peak Expiratory Flow Rates
- Measurements of peak expiratory flow rates (PEF) at work and away from home can be helpful in the diagnostic evaluation of occupational asthma 2, 3, 4, 5, 6.
- Serial measurement of PEF is considered the most appropriate initial confirmatory test for occupational asthma, with recordings taken every 2 hours during waking hours, both on days at and away from work 2.
- A minimum positive record includes recordings taken over two work periods and two rest periods, and a minimum negative record will also include a rest period of at least 10 days duration 2.
Interpretation of Peak Expiratory Flow Records
- Expert visual assessment of plotted records appears to be the most specific and sensitive method of interpretation, but it requires experience and involves qualitative judgements 2, 6.
- Statistical methods can also be used to detect differences between recordings at and away from work, but may not be as sensitive or specific as visual analysis 3, 6.
- Factors that may interfere with interpretation include intermittent exposure to suspect agents at work, irregular medication, irregular timing of the first reading after waking, respiratory tract infection, and variable patient peak expiratory flow measurement technique 2.
Frequency of Peak Expiratory Flow Measurements
- Recording PEF every two hours results in a slightly more satisfactory agreement between readers and in concordance in terms of sensitivity/specificity than less frequent PEF readings 4.
- However, four times a day assessment is almost as satisfactory, and may be more practical for patients to perform 4.
- The optimum number of recordings per day to achieve the best between-reader and within-reader reproducibility and sensitivity/specificity ratio is still unknown, and further studies are required to determine this 4.
Limitations and Future Directions
- Limitations of PEF monitoring include the low sensitivity of PEF to detect mild changes in airway calibre, the blunting effect of pharmacological treatment, and the compliance and honesty of the subject 3.
- Further studies are required to select the best indices of daily and day-to-day variability to be used in the evaluation of PEF changes between work and out-of-work periods, and to quantify the judgements involved in interpreting PEF records 2, 3.