Statistical analysis
Mean, standard deviation, ranges, median, range, frequency, and ratio data were calculated as descriptive statistics. The Kruskal–Wallis and Mann–Whitney U tests were used for the analysis of numerical independent data. Receiver operating characteristic (ROC) curves were set up to identify the cut off value for KL6 to differentiate patients with and without ILD, matching with the Youden method33,34, which detect sensitivity and specificity. Estimation of the area under the ROC curve and its 95% confidence interval, Sensitivity, specificity, positive and negative predictive values related with the cut off value were all calculated. All statistical analyses were applied using SPSS for Windows 15 statistical software. A value of p<0.05 was statistically significant, a value of p<0.001 was highly statistically significant, and a value of p>0.05 was non-statistically significant.