Introduction The MRC dyspnoea scale consists of five grades that contain of a description of more than one activity. The comparability of these components is not known. This study aimed to examine the performance of individual descriptions of each MRC grade.

Methods Phase I: cognitive debriefing with COPD patients was conducted to elicit their understanding of each activity (10 items) of the five MRC grades. Phase II: COPD patients completed the MRC scale (grades 1–4) and a MRC-Exploded (MRC-Ex) version consisting of 10-items, each representing one MRC activity. Each item used a 4-point response scale (0 ‘not at all’ to 4 ‘all of the time’). Rasch analysis was used to assess the pattern of MRC-Ex item severity (logit) to assess the appropriateness of combining individual activity descriptors into single MRC grades.

Results 36 patients participated in cognitive debriefing. Key issues identified: MRC 1: unclear what constituted ‘strenuous exercise’ and does not represent mild severity and MRC 5: ‘too breathless to leave the house’ viewed as “much worse than being breathless with dressing”. 203 patients completed Phase II (mean age 64.7 SD 7.5 years, GOLD: 1:14% 2:41% 3:25% 4:7%). The easiest item to affirm was ‘walking up a slight hill’ (logit −2.76) and “too breathless to leave the house” was the most difficult (logit 3.42) (Table 1). MRC components in grade 5 are not of equivalent severity - at least 2 logits apart.

Conclusions This study highlight the importance of context when using the MRC. Grade 1 “strenuous exercise” is unlikely to yield a reliable response from patients diagnosed with COPD. Secondly, if data collection is taking place outside of the home then it is pointless to ask respondents if they are too breathless to leave the house; on the other hand, if studying patients who may require palliative care services, that might well be relevant. For contexts where it would be relevant, we suggest separating Grade 5 components: “leave the house” and “dressing/undressing”.