Asthma and occupation: Diagnosis using serial peak flow measurements

Asma e trabalho: diagnóstico por medida seriada do peak flow

Evidence collection method

This guideline followed the standard of a systematic review with evidence retrieval based on evidence-based medicine (EBM), so that clinical experience is integrated with the ability to critically analyze and apply scientific information rationally, thus improving the quality of medical care.

We used the structured mode of formulating questions synthesized by the acronym PICO, where P stands for patients with occupational asthma, I for indicator i.e. serial peak flow measurement, and O stands for the outcome of diagnosis.

By raising a relevant question related to the proposed topic, we identified, based on the structured question, the keywords that formed the basis of the search for evidence in the databases: Medline-Pubmed, Lilacs, Labordoc and Cochrane Library. The studies had their abstracts reviewed and after applying the eligibility criteria (inclusion and exclusion), 33 articles were selected in order to answer the clinical doubt (Annex I).

Clinical question

Is there repercussion on clinical outcomes when applying serial peak flow measurements to diagnose work-related asthma among workers with respiratory symptoms?

Grades of recommendation and levels of evidence

• A: Experimental or observational studies of higher consistency.

• B: Experimental or observational studies of lower consistency.

• C: Case reports / non-controlled studies.

• D: Opinion without critical evaluation, based on consensus, physiological studies or animal models.

Objective

This Guideline aims to present and discuss the best scientific evidence currently available regarding the clinical outcomes of work-related asthma diagnosis using a serial peak-flow measure for workers with respiratory symptoms.

Introduction

Occupational asthma (OA) is a form of work-related asthma (WRA) characterized by reversible airflow obstruction, bronchial hyperreactivity and airway inflammation, and may be mediated by immunological or non-immunological reactions, resulting from conditions attributable to a certain etiological factor in the work environment. According to population-based studies, OA is estimated to account for about 10 to 25 percent of adult asthma.^1-3

In this context, OA is characterized as asthma beginning after exposure to an etiologic factor in the work environment, but there is also another form of WRA that is characterized by pre-existing asthma aggravated or exacerbated as a result of an agent present in the work environment called work aggravated asthma (WAA).

Part of the problem that involves WRA comes from the analysis of observational studies which, in comparing the incidence of this pneumopathy with the records of notifications in several countries, objectively verified its underdiagnosis.^4-9

Thus, WRA underdiagnosis generates impacts on workers' health, with impairment of quality of life and work capacity, and on economic indicators such as workplace absenteeism and consumption of health resources.^10,11

In any case, for an adequate diagnosis of WRA, it is essential that the relation between signs and symptoms in an individual with occupational exposure is well established as early as possible. Diagnostic methods for WRA include serial peak flow measurement that is intended to monitor airflow limitation in the presence (period worked) and absence (non-working time) of possible risk factors in the work environment.

In the technical analysis of a diagnostic test, there are some requirements that need to be met for incorporation into medical practice. They include adequate sensitivity (percentage of positive results in a group presenting the disease) and specificity (percentage of negative results in a healthy group). In addition, the diagnostic test should contribute to adequate treatment in order to promote objective modification in the natural history of the disease.¹²

Therefore, given the magnitude, underdiagnosis and impact of WRA in the clinical practice of the occupational physician, this guideline is intended to present and discuss the best available scientific evidence on the effectiveness of WRA diagnosis using serial peak flow measurement for workers with respiratory symptoms.

Data extraction

Is there repercussion on clinical outcomes when applying serial peak flow measurements to diagnose work-related asthma among workers with respiratory symptoms?

The selected articles were reviewed in order to calculate the sensitivity and specificity for WRA diagnosis. We found a sensitivity of 82% (95CI 76-90%) and a specificity of 88% (95CI 80-95%).^13-40 (B)

The gold standard used in the diagnostic test studies was broncoprovocation with specific agents and forced expiratory volume measurement in the first second (FEV1). FEV1 was more sensitive to assess asthma alterations than peak flow; however, respiratory maneuvers for FEV1 were considered less reliable when not personally supervised by a health professional and thus less reproducible in cases of serial measurements at work and outside work. In contrast, serial peak flow measurements were more reliable and more reproducible in the unsupervised diagnostic format.⁴¹ (A)

For adequate assessment, in an individual with suspected WRA, serial peak flow measurements should be indicated at the onset of the pulmonary condition and should monitor airflow limitation during the work period compared to periods away from work. A wide variety of specific protocols have been described for satisfactory measurement, including peak flow measurements at least four times a day over two weeks at the workplace, presumably due to respiratory symptoms, and for two weeks in settings away from the work environment.⁴² (A)

The rate of return of serial peak flow measurements was adequate containing 61% of measures returned for analysis with interpretable and acceptable data for WRA diagnosis.⁴¹ (A)

The rate of return of serial measurements can be improved when the employee receives face-to-face instructions rather than only written instructions. In addition, the result can be further optimized when the employee uses a registration card to point out measurement frequencies and periods.⁴¹ (A)

Data interpretation can be performed with visual analysis of the information by a trained specialist. However, software-based interpretation improves data analysis.⁴¹ (A) One of the softwares available for analysis of serial peak flow measurements is Oasys.

Limitations of the application of serial peak flow measurements include: the need for worker collaboration to obtain satisfactory records, the presence of functional illiteracy rendering it impossible to record the information, and the non-applicability of the method to severe episodes of asthma while in the work environment.^41,43,44 (A)

However, when these potential sources of error are understood, serial peak flow measurement is a viable, useful and low-cost method for diagnosing WRA, mainly due to adequate specificity, sensitivity, rate of return of the measurements, possibility to analyze other differential diagnoses and possibility of associating labor activity with the presence of respiratory symptoms.⁴⁵ (A)

Diagnosis of WRA is largely important for both primary prevention and tertiary prevention in the workplace. Regarding primary prevention, even the diagnostic elucidation of a single case of WRA in a group of workers sharing similar occupational exposures offers the possibility of reassessing occupational hazards in the workplace, thereby offering individual and/or collective protective measures to prevent the incidence of new cases. As for tertiary prevention, the diagnostic elucidation of WRA in a specific case subsidizes the occupational physician with technical information to guarantee the control of presumed factors in the work environment that might be generating disease, exacerbation or aggravation and, thus, allow decision-making, in the sense of avoiding the presumed exposure with professional rehabilitation or readaptation of specific cases in a different work location.⁴² (A)

Recommendation

The analysis of the selected articles indicates that there is sufficient scientific evidence to strongly recommend the application of serial peak flow measurements with a moderate impact on the diagnosis of work-related asthma. Serial peak flow measurement should be applied in the presence of suspected work-related asthma, i.e. when there are respiratory symptoms. Thus, our recommendation is to use the method in a diagnostic format, which does not apply to asymptomatic populations in the screening format.

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Publication Dates

• Publication in this collection
  Feb 2018

History

• Accepted
  12 May 2017