Spirometry reference values for American Indian adults - Results from the Strong Heart Study

Study objective: To derive spirometry normative values from a large populat ion of American Indian adults and compare them to reference values for whit e adults. Design: Pulmonary function was assessed using spirometry in participants of the Strong Heart Study, a multicenter, community-based, prospective study of cardiovascular risk factors and disease in American Indians, utilizing A merican Thoracic Society guidelines and a vigorous quality assurance progra m. Setting: Central Arizona, southwestern Oklahoma, central South Dakota, and northeastern North Dakota. Participants: Acceptable spirometry results were obtained from 1,619 women and 1,005 men aged 45 to 74 years. Results: Internal reference values and normal ranges for FEV1, FVC, and the FEV1/FVC ratio were derived from a healthy subgroup of 253 women and 190 m en, identified by excluding participants with factors associated with a low er FEV, Ten percent of the entire cohort (269 of 2,624 subjects) had airway s obstruction, as defined by an FEV1/FVC below the lower limit of the norma l (LLN) using the internal reference equations. After allowing for measurem ent "noise," 31 participants were below the LLN using reference equations f or white adults from the large National Health and Nutrition Examination St udy (NHANES) III study but were normal using the internal reference equatio ns (1.3% false-positive), while 27 participants were classified as normal u sing NHANES III equations but had airways obstruction using the internal re ference equations (1.2% false-negative). Similarly low misclassification ra tes were seen for a low FVC (prevalence, 17.6%). Conclusion: For clinical purposes, NHANES III spirometry reference equation s for white adults may be used when testing American Indian women and men a ged 45 to 74 years.