Interpretation of pulmonary function tests basically depends on prediction of normal values derived from equations using non-deformed body height. In many patients body height can not be accurately measured. The arm-span method has been used for estimating body height, but the normal relationship between body height and arm span is not exact and differs in various ethnic groups and even between two genders of the same race. In order to minimise the error of estimation of non-deformed body height, the normal relationship between body height and arm span was determined for 754 Persian males and 708 females aged 7 to 82 years, all having normal body stature. In accordance with earlier reports, two sets of spirometric parameters derived once from height, sex, age; and again from arm-span, sex, age were statistically different, and overestimated when the measured arm-span was used. The body-height/arm-span relationship is described using linear regression equations; in subgroups aging 20 years or less and those older than 20 in different genders. The results indicate significant sex and age differences in the arm-span/height ratio. Two sets of spirometric parameters predicted by real height, sex, age/and predicted height, sex, age were not statistically different for most of the parameters especially vital capacity.
In conclusion: height estimated from arm span, performs much better than arm span to predict pulmonary function parameters.