MedWire News: A new method of analysis developed to detect late asthmatic reactions following specific inhalation testing complements other validated methods of peak expiratory flow (PEF) measurements for the diagnosis of occupational asthma, research shows.

The time-point analysis method had good sensitivity and high specificity when there were at least two time points with significant work-day deterioration and at least four time points for comparison.

The results of the study, by Cedd Burg (Birmingham Heartlands Hospital, Bordesley, UK) and colleagues, are published in the journal Thorax.

With occupational asthma, clinical guidelines recommend confirmation of the diagnosis with serial measurements of PEF. The researchers note, however, that once occupational asthma has developed, many factors can influence the PEF, including sleep, treatment, exercise, and respiratory infections.

"The difficult part is to separate changes due to work – which are often delayed and cumulative – from those due to other confounding factors," Burg and colleagues point out. Increasing the sensitivity of serial PEF measurements is therefore a priority.

With the new diagnostic test, investigators used a time-point analysis originally developed to detect late asthmatic reactions following specific inhalation testing.

Using records from 236 workers with occupational asthma and 320 controls, the rest-day measurements were obtained from an analysis of variance by time. Work-day PEF measurements were averaged into matching 2-hour time segments.

Records with two or more time points significantly lower on work than rest days had a sensitivity of 67% and a specificity of 99% for the diagnosis of occupational asthma. Reducing the requirements to at least one non-waking time point difference increased sensitivity to 77% but reduced specificity to 93%.

Specific inhalation testing is the current gold standard for diagnosing occupational asthma. A positive test is usually defined as one or two measurements following exposure which are 15% to 20% below an appropriate control exposure.

The researchers noted that occupational asthma is currently widely underdiagnosed, at least in part from the lack of specialist expertise.

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