Global lung function initiative: Reference equations for the transfer factor for carbon monoxide (TLCO)

Abstract

Background: There are numerous reference equations available for transfer factor for carbon monoxide (TLCO); however there are currently no recommendations as to which equation should be used in clinical practice. We aimed to develop The Global Lung Function Initiative (GLI) all-age, multi-ethnic reference values for TLCO. Methods: Data from 19 centres in 14 countries from studies published after the year 2000 were combined. Reference equations were derived using the LMS method and the GAMLSS program. Results: A total of 12 660 TLCO measurements from asymptomatic, lifetime non-smokers from 4 to 91 years of age were available. Eighty-five percent of the data submitted were from Caucasian subjects. Following adjustments for elevation above sea level, and the assumptions used for calculating the anatomic dead space volume there was a high degree of overlap among the datasets. All data were uncorrected for haemoglobin. Reference equations were derived for TLCO, carbon monoxide update from the lung (KCO) and alveolar volume (VA). The limited data in non-Caucasians limited the development of equations for Caucasians subjects only. Conclusion: This is the largest collection of normative TLCO data, and the first robust global reference equation available for TLCO. The variations among disparate TLCO datasets can be reduced by taking into account methodological considerations. Results are presented on behalf of the GLI TLCO working group.