Values for transfer factor of the lung for carbon monoxide (TLCO), transfer coefficient (KCO) and alveolar volume (VA) as calculated using the different reference equations

TLCO % pred#Z-scoreKCO % predZ-scoreVA % predZ-score
GLI [1]37% (29–46)−5.064% (52–73)−2.560% (53–69)−3.5
ECSC [10]35% (28–44)−3.966% (55–78)−1.855% (48–64)−4.1
Crapo [11]30% (24–38)−4.455% (46–64)−2.554% (47–62)−4.0
Miller [12]36% (29–45)−3.365% (54–75)−1.955% (48–63)−3.5
NHANES-1 [13]33% (26–41)

Data are presented as median % predicted values with interquartile ranges. The Z-score represents the difference between the measured value and the reference population mean in standard deviation units. For example; a Z-score of −3 means that the measured value is far below the 2.5th percentile in a healthy population. #: TLCO % predicted values from all older equations were significantly lower than the Global Lung Function Initiative (GLI) TLCO % predicted (p<0.001, Wilcoxon signed ranks test). : Z-scores, KCO % predicted and VA % predicted could not be calculated. ECSC: European Community for Steel and Coal; NHANES-1: National Health and Nutrition Examination Survey 1971–1975.