Over-adjustment Bias: AST, total bilirubin, and LDH had moderate associations with hemoglobin-adjusted DLCO(%pred). However, total hemoglobin itself had significant associations with AST, T-Bili, and LDH. The association between those lab results and hemoglobin-adjusted DLCO(%pred)  was biased and primarily contributed by the correlation among lab results and with total hemoglobin. This type of error is known as over-adjustment bias. The bias was further established when those lab estimates demonstrated no association with DLCO corrected for V_A (instead of hemoglobin). Hence, AST, T-Bili, and LDH were not included in XGBoost or regression analysis as potential predictors of adjusted DLCO.

P-values <0.05 were considered significant. R: Pearson correlation coefficient, CI: confidence interval, V_A: alveolar ventilation.