Sylvia Verbanck1, Daniel Schuermans2, Bruce R Thompson3,4, Eef Vanderhelst2. 1. Respiratory Division, University Hospital UZ Brussel, Vrije Universiteit Brussel, Brussels, Belgium, sylvia.verbanck@uzbrussel.be. 2. Respiratory Division, University Hospital UZ Brussel, Vrije Universiteit Brussel, Brussels, Belgium. 3. Allergy, Immunology, and Respiratory Medicine, Alfred Hospital, Melbourne, Victoria, Australia. 4. School of Health Sciences, Swinburne University of Technology, Melbourne, Victoria, Australia.
Abstract
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.
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.