Spirometry reference values for American Indian adults: results from the Strong Heart Study.

STUDY
OBJECTIVE: To derive spirometry normative values from a large population of American Indian adults and compare them to reference values for white 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 American Thoracic Society guidelines and a vigorous quality assurance program.
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 FEV(1), FVC, and the FEV(1)/FVC ratio were derived from a healthy subgroup of 253 women and 190 men, identified by excluding participants with factors associated with a lower FEV(1). Ten percent of the entire cohort (269 of 2,624 subjects) had airways obstruction, as defined by an FEV(1)/FVC below the lower limit of the normal (LLN) using the internal reference equations. After allowing for measurement "noise," 31 participants were below the LLN using reference equations for white adults from the large National Health and Nutrition Examination Study (NHANES) III study but were normal using the internal reference equations (1.3% false-positive), while 27 participants were classified as normal using NHANES III equations but had airways obstruction using the internal reference equations (1.2% false-negative). Similarly low misclassification rates were seen for a low FVC (prevalence, 17.6%).
CONCLUSION: For clinical purposes, NHANES III spirometry reference equations for white adults may be used when testing American Indian women and men aged 45 to 74 years.