Spirometric reference values in a large Middle Eastern population

Ethnic differences in pulmonary function have been frequently reported. The purposes of this study were to derive equations for the prediction of normative spirometry values for a large population of Persians in Isfahan and compare them to reference values from a White Euro-USA population. Spirometry measurements were obtained from 4,341 randomly selected healthy nonsmoker subjects in Isfahan, Iran, utilising American Thoracic Society guidelines and a vigorous quality assurance program. Measured data from 3,213 subjects were analysed using multiple regression techniques to derive prediction equations for spirometric variables; the remaining 1,128 subjects were used as a control group to test the validity of the derived equations. In addition, predicted values were compared with values derived from recently published equations for the USA. Derived prediction equations showed good performance for most spirometric parameters. Compared with USA Whites, adult Persians have minimally lower forced vital capacities, while the values for children are close to USA Whites. In comparison with reference equations based on European or USA populations, local reference values are more biologically and technically suitable for the interpretation of spirometric data from Iranian populations.