Referential equations for pulmonary diffusing capacity generated from the Japanese population using the Lambda, Mu, or Sigma method and their comparisons with prior referential equations

This study aimed to establish reference equations for single-breath lung carbon monoxide diffusing capacity (DLCO), alveolar volume (VA), and transfer coefficient of the lungs for carbon monoxide (KCO, sometimes written as DLCO/VA) in the Japanese population. A generalised additive model for location size and shape (GAMLSS) was used to build each equation. To collect pulmonary function data throughout a broad age range, we prospectively obtained pulmonary function data from healthy volunteers and retrospectively obtained data from patients with normal diffusing capacity aged 16–85 years. In total, 702 tests were conducted. The validation group z-scores, except for DLCO in males, showed substantial discrepancies between the Global Lung Initiative (GLI) baseline prediction equations and the present study’s prediction equations, indicating the need for a new reference value prediction approach. The root mean square errors of the DLCO, VA, and KCO reference values obtained from the present study’s prediction equations were lower than those derived from the GLI and previous linear regression equations. Reference values obtained in this study were more appropriate for our sample than those derived from the existing baseline prediction equations. This research’s contribution is the development of a more precise prediction equation that can be used to establish a reference value range for pulmonary diffusing capacity. This research does not include any dissemination plan (publications, data deposition and curation).