Aligning Lung Function Equipment and Reference Values in Adults

• Published in: Respiration Vol. 98; no. 3; pp. 246 - 252
• Main Authors: Verbanck, Sylvia, Schuermans, Daniel, Thompson, Bruce R., Vanderhelst, Eef
• Format: Journal Article
• Language: English
• Published: Basel, Switzerland S. Karger AG 01.09.2019
• Subjects: Adaptation (Physiology); Basic Science Investigations; United States; Lung function indices; Global Lung Function Initiative; Limits of normal; Reference values
• ISSN: 0025-7931; 1423-0356; 1423-0356
• DOI: 10.1159/000501283

Background: When introducing new equipment or reference equations into the lung function laboratory, systematic z-score deviations could arise due to local differences in population or equipment. Objective: To propose a workable method for aligning reference equations with lung function equipment. Method: Using two cases of equipment transition in our laboratory as a test case, we first performed lung function testing after the transition, on a control group of 40 normal young adults (20 male/20 female; 20–30 years old). For those indices with an average z-score in excess of ±0.5, adapted reference values were obtained by an offset or scaling factor on the M coefficient with the so-called lambda-mu-sigma (LMS) method recommended by the Global Lung Function Initiative, and the z-scores were computed again. Results: Following a transition involving instrumental dead space reduction, the lung clearance index was predictably reduced, resulting in a mean (±SD) z-score of –1.9 (±1.1) in the control group; by adapting the reference values with an offset on M, the z-score became –0.1 (±1.1). Applying the same method to a transition of standard lung function equipment, the z-scores became centered around zero in the control group, but also became properly aligned in a test group of 81 other subjects spanning a wider age range (20–80 years). Conclusions: We proposed and verified a method for aligning local equipment with reference values obtained elsewhere, or following a local change in equipment. The key is to measure a relatively small young adult group, identifying those lung function indices that need adaptation based on z-scores, in order to then obtain laboratory-specific reference values that can be applied over the entire age range.