Assessment of the value of 6-minute walk test to predict the severity of interstitial lung disease among Indian patients

Sir, In the January to March 2024 issue of The Journal of Association of Chest Physicians, Sompalli et al.[1] found high sensitivity and specificity of the 6-minute walk test (6MWT) to predict the severity of interstitial lung disease (ILD) among Indian patients. The three parameters of the 6MWT, namely distance, oxygen saturation before, and oxygen saturation after the test, were significantly reduced and served as independent predictors of severe ILD. Sompalli et al.[1] effectively addressed several study limitations. We present another worthy limitation. The 6MWT is a submaximal exercise test broadly used in clinical settings to assess physical capacity in healthy and sick individuals. To have a sound interpretation of 6MWT values, it is critical to compare the estimated value for a particular patient with a normal one appropriate for that population necessitating the use of reference values (RVs) of 6MWT. Based on numerous determinants such as age, gender, height, weight, race, and socioeconomic background,[2] numerous populations have developed their 6MWTRVs.[3,4] Interestingly, India has formulated its 6MWTRVs for use in research institutions and clinical setups.[5] In the study methodology, Sompalli et al.[1] amazingly stated that they referred to the American Thoracic Society guidelines, primarily set for the Caucasian population, rather than the local 6MWTRVs to evaluate the estimated 6MWT values in the studied population. As a result, the study findings might be additionally precluded by that methodological limitation.