People with interstitial lung disease (ILD) often experience disabling symptoms, which impairs their functional capacity, further
accelerating disease progression. The 6-minute walk test (6MWT)
has been the most widely used field test to assess functional capacity and to discriminate the mortality risk in people with ILD.
Nevertheless, its application across settings (e.g., patients’
homes) is often limited due to the need of a 30 m corridor. Alternatives to assess functional capacity in these settings have been
emerging, such as the 1-minute sit-to-stand test (1-minSTS) and
the Chester step test (CST). However, the first does not allow
exercise prescription. The CST is a simple and low-cost field test,
which enables exercise prescription and requires minimal physical
space to assess functional capacity. Its suitability to be used as a
first-line screening tool to detect functional capacity impairment
and mortality risk in people with ILD is however unknown. Thus,
the aim of this study was to determine the discriminative ability
of the CST in distinguishing people with ILD with or without functional impairment and low or higher risk of mortality. A retrospective cross-sectional study was conducted with stable (i.e., no history of acute cardiac events, acute exacerbations or other
respiratory complications in the previous month) people with ILD.
The following measures were collected: CST, 6MWT and 1-minSTS.
A receiver operating characteristics (ROC) curve analysis was performed and area under the curve (AUC), sensitivity, specificity and
accuracy were calculated. We determined a threshold for the CST
to identify: i) functional impairment, based on published cut-offs
of the percentage predicted of the 1-minSTS and the 6MWT (both
70% predicted); and, ii) mortality, based on different established
cut-offs of the 6MWT (250, 330 and 350 m). The optimal cut-off
points were identified by the highest Youden index. Eighty-three
people with ILD (65 ± 14 years old; 45 [54.2%] female; FVC 77.7 ±
17.9%predicted; DLCO 50.3 ± 20.7% predicted) were included in
the analysis. The cut-off points of the 1-minSTS (AUC = 0.73; 95%CI
0.63-0.84; 81% sensitivity; 65% specificity; accuracy = 0.72) and
6MWT (AUC = 0.91; 95%CI 0.82-0.99; 88% sensitivity; 83% specificity; accuracy = 0.86) identified a cut-off of 40.5 steps in CST to
detect functional impairment in people with ILD. All cut-offs of
the 6MWT identified a cut-off of 36 steps on the CST (6MWT <
250m: AUC = 0.89; 95% CI 0.80-0.97; 86% sensitivity; 80% specificity; accuracy = 0.80; 6MWT < 330m: AUC = 0.97; 95%CI 0.93-1; 96%
sensitivity; 81% specificity; accuracy = 0.90; 6MWT < 350m: AUC =
0.93; 95%CI 0.86-1; 98% sensitivity; 70% specificity; accuracy =
0.90) to detect increased risk of mortality. Healthcare professionals may now use cut-offs of 40.5 and 36 steps in the CST to accurately detect people with ILD with functional impairment and/or
at increased risk of mortality, respectively, which may contribute
to the implementation of tailored and preventive interventions to
improve functional capacity and reduce the risk of mortality in
this population.publishe