Defining high probability when making a diagnosis of asthma in primary care: mixed-methods consensus workshop

Objective: Making the diagnosis of asthma is challenging. Guidelines recommend that clinicians identify a group at 'high probability' of asthma. High probability, however, is not numerically defined giving rise to uncertainty. The aim of this work was to build consensus on what constitutes a high probability of asthma in primary care. High probability was defined as the probability threshold at which there is enough information to make a firm diagnosis of asthma, and a subsequent negative test would not alter that opinion (assumed to be a false negative).

Design: Mixed-methods study.

Setting: A consensus workshop using modified nominal group technique was held during an international respiratory conference.

Participants: International conference attendees eligible if they had knowledge/experience of working in primary care, respiratory medicine and spoke English.

Methods: Participants took part in facilitated discussions and voted over three rounds on what constituted a high probability of asthma diagnosis. The workshop was audio-recorded, transcribed and qualitatively analysed.

Results: Based on final votes, the mean value for a high probability of asthma in primary care was 75% (SD 7.6), representing a perceived trade-off between limiting the number of false positives (more likely if a lower threshold was used) and pragmatism on the basis that first-line preventive therapies (ie, low-dose inhaled corticosteroids) are relatively low risk. The need to review response to treatment was strongly emphasised for detecting non-responders and reviewing the diagnosis.

Conclusion: A consensus probability of 75% was the threshold at which the primary care participants in this workshop felt confident to establish the diagnosis of asthma, albeit with the caveat that a review of treatment response was essential. Contextual factors, including availability and timing of tests and the ease with which patients could be reviewed, influenced participants' decision making.