The methacholine challenge test protocol was assessed in the reanalysis of three occupational studies. We evaluated the impact of truncating the range of methacholine on responsiveness, as defined by slope and PC20. In original analysis, reactivity was similar for apprentices and auto body shop workers, whereas boilermakers were more responsive. Truncating high concentrations did not change the classification of subjects with PC20 <8 or 16 in any population. However, when responsiveness was measured by slope, the mean responsiveness increased, from −7.9 to −15.3 for apprentices and −7.2 to −10.0 for auto-body shop workers. Results support the American Thoracic Society’s recommended maximum of 16 mg/mL and provide evidence that extending the dose range beyond that does not increase sensitivity, whereas stopping before 16 may exaggerate response. Furthermore, to ensure validity, neither slope nor PC20 should be extrapolated beyond data.
From the Department of Work Environment, University of Massachusetts, Lowell, Massachusetts (Dr Agalliu, Dr Eisen, Dr Wegman); Department of Environmental Health (Occupational Health Program), Harvard School of Public Health, Boston, Massachusetts (Dr Eisen, Dr Hauser, Dr Christiani); Yale Occupational and Environmental Medicine Program, Yale University School of Medicine, New Haven, Connecticut (Dr Redlich, Dr Stowe, Dr Cullen); and School of Occupational and Environmental Hygiene, University of British Columbia, Vancouver, BC, Canada (Dr Kennedy).
Address correspondence to: Dr Ellen A. Eisen ScD, Department of Work Environment, University of Massachusetts Lowell, One University Avenue, Kitson 200, Lowell, MA 01854; e-mail address: Ellen_Eisen@uml.edu.
This publication was made possible by grants CDC-NIOSH (R01H3457) and (OH00152) and was also supported by the NIH-NCRR-GCRC program M01-RR00125 (Yale).