Evaluation of the performance of the reference equations for single-breath diffusing capacity of the lung for carbon monoxide (DLCOsb) in Latin American populations at different altitudes: A multicentre study.

Introduction: Altitude, a factor not considered in most reference equations for single-breath diffusing capacity of the lung for carbon monoxide (DLCOsb), plays a crucial role in its assessment. This variable is particularly relevant for Latin American populations residing at different altitudes.

Methods: This analytical, prospective, multicentre study was conducted in Latin American adults living at low and high altitudes with normal spirometry. Healthy, asymptomatic subjects were identified through the PLATINO survey. To determine the model with the best performance based on standard estimated error (SEE), predicted DLCOsb values were obtained using the Vásquez García, Crapo, García Rio, and Global Lung Function Initiative (GLI) equations.

Results: A total of 269 subjects were included: 90 at low altitude and 179 at high altitude. Women comprised 66.9% (180/269), and the median age was 34 years (IQR 25-51). At both sea level and high altitude, the Vásquez García equation, which includes haemoglobin (Hb), showed the best predictive performance. In both settings, GLI-predicted values were lower than measured values (SEE: 2.158 at low altitude and 5.1 at high altitude).

Conclusions: Although with wide limits of agreement for all models, Vázquez-García's equation shows the best performance in the interpretation of DLCOsb in Latin American populations residing at any altitude. Even with adjustments for altitude and Hb, the GLI model underestimates the predicted values of DLCOsb and could require an adjustment factor or inclusion of the altitude variable in the model's new version.