Modified BODE indexes: Agreement between multidimensional prognostic systems based on oxygen uptake

Abstract

Aim: It has been recently shown that the original BODE index has a high degree of correlation with two modified BODE indexes using maximal oxygen uptake expressed either as mL/min/kg (mBODE) or as the percentage predicted (mBODE%). In this study we investigated the agreement between the two modified BODE indexes (mBODE and mBODE%) in patients with stable chronic obstructive pulmonary disease (COPD).

Methods: A total of 169 patients with stable COPD were enrolled in this cross-sectional study. Differences between the two mBODE indexes were assessed using kappa coefficients and Bland-Altman plots. One out of every three patients underwent the six-minute walking test to investigate the agreement with the original BODE index.

Results: Correlations between the two mBODE indexes with each other (r = 0.96, P < 0.001) and with the original BODE index (mBODE r = 0.88, P < 0.001; mBODE% r = 0.93, P < 0.001) were excellent. However, the two mBODE indexes were significantly different from each other (mBODE 5.27 +/- 2.3 versus mBODE% 4.31 +/- 2.5; P < 0.001). The kappa coefficients were significantly lower (entire study group k = 0.5, P < 0.001) for every GOLD stage. The mean difference between the two mBODE indexes was 0.8 +/- 0.6 units. Differences with the original BODE were higher for the mBODE (1.8 +/- 0.9) than for the mBODE% (0.6 +/- 0.8).

Conclusions: The new mBODE indexes are highly correlated but significantly different from each other. The differences between the novel indexes deserve further scrutiny.

Keywords: BODE index; chronic obstructive pulmonary disease; exercise testing; multidimensional evaluation; oxygen uptake.

Figure 1

Scattergram and regression line showing a highly significant correlation between the two modified BODE indexes (r = 0.96, P < 0.001).

Figure 2

Bland-Altman plots exploring the differences between the two modified BODE indexes in A) the entire study cohort, as well as in B) patients with GOLD I–II, C) GOLD III, and D) GOLD IV. Mean differences: entire cohort: 0.95 (−0.46–2.37); GOLD I–II: 1.1 (−0.41–2.63), GOLD III: 1 (−0.35–2.35), and GOLD IV: 0.7 (−0.5 –1.98) units.

Figure 3

Scattergram and regression line showing a highly significant correlation between the original BODE and A) mBODE (r = 0.88; P < 0.001), as well as B) the mBODE% (r = 0.93; P < 0.001).

Figure 4

Bland–Altman plots exploring the differences between the original BODE and A) mBODE, mean difference 1.8 (0.03–3.77), as well as B) the mBODE%, mean difference 0.6 (−1.1–2.32).