Reduction in T LCO and survival in a clinical population.

Abstract

How best to express the level of transfer factor of the lung for carbon monoxide (T LCO) has not been properly explored. We used the most recent clinical data from 13 829 patients (54% male; 10% non-European ancestry; median age 60.5 years, range 20-97 years; median survival 3.5 years, range 0-20 years) to determine how best to express T LCO function in terms of its relationship to survival. The proportion of subjects of non-European ancestry with Global Lung Function Initiative (GLI) T LCO z-scores above predicted was reduced, but was significantly increased between -1.5 and -3.5, suggesting the need for ethnicity-appropriate equations. Applying GLI forced vital capacity (FVC) ethnicity methodology to GLI T LCO z-scores removed this ethnic bias and was used for all subsequent analysis. T LCO z-scores using the GLI equations were compared with Miller's USA equations with median T LCO z-scores being -1.43 and -1.50 for GLI and Miller equations, respectively (interquartile range -2.8 to -0.3 and -2.4 to -0.7, respectively). GLI T LCO z-scores gave the best Cox regression model for predicting survival. A previously proposed six-tier grading system for level of lung function did not show much separation in survival risk in the less-severe grades. A new four-tier grading based on z-scores of -1.645, -3 and -5 showed better separation of risk with hazard ratio for all-cause mortality of 2.0, 3.4 and 6.6 with increasing severity. Applying GLI FVC ethnicity methodology to GLI T LCO predictions to remove ethnic bias together with a new four-tier z-score grading best relates T LCO function to survival.