Abstract
Introduction: Sputum colour charts (SCC) are used in the follow-up of patients with bronchiectasis. The best known are the chart by Murray et al. (mSCC) with 3 categories and the one by Stockley et al. (sSCC) with 9 categories. (1,2) We compared these SCC with a new chart containing 17 categories (nSCC)(abstract n° 852384), comparing intra-rater reliability (IntraRR) and inter-rater reliability (InterRR).
Methods: Twenty cystic fibrosis patients were asked to collect their morning sputum. All samples were scored 5 times in a random order by 2 blinded raters, scoring for the 3 SCC. IntraRR and InterRR was analyzed by calculating the kappa.
Results: All 3 charts had significant IntraRR (all p<0.0001). The highest IntraRR was seen for mSCC (κrater1=0.91 and κrater2=0.78). Similar IntraRR was seen for the other charts (sSCC κrater1=0.62 and κrater2=0.63; nSCC κrater1=0.72 and κrater2=0.65). The InterRR was high for the mSCC (p<0.0001; κ=0.91), lower but significant for the sSCC (p=0.037; κ=0.59) and not significant for the nSCC (p=0.15; κ=0.26). Plotting out number of categories and p-value, we estimate that the p=0.05 threshold lies at ten categories.
Conclusion: Higher InterRR is seen when the SCC contains less categories. IntraRR reliability was independent of number of categories. SCC cannot contain more than 10 categories to remain reliable.
1 Murray MP et al. Eur Respir J 2009;34:361-4
2 Stockley RA et al. Thorax 2001;56:366-72.
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