Interpreting spirometric data - Impact of substitution of arm span for standing height in adults from North India

Study objective: To evaluate if direct substitution of arm span for height during interpretation of spirometry data leads to any significant statistical. or clinical differences in Indian adults, and to compare this method with the use of height estimated indirectly from arm span. Design: Cross-sectional. Setting: Respiratory laboratory of a tertiary referral hospital in North India. Participants: Two hundred twenty-eight subjects referred for spirometry. Measurements and results: Standing height and arm span were measured for all subjects. Spirometry measurements included FVC, FEV1, FEV1/FVC, peak expiratory flow, and maximal midexpiratory flow. Predicted values for each parameter were calculated separately for height, arm span, and height estimated from fixed height:arm span ratio. Results were classified into normal, obstructive, and restrictive defects for each height, arm span, and estimated height measurement, and any abnormality was categorized as mild, moderate, or severe. Arm span exceeded height in 182 (79.82%) subjects. Thirty-seven (16.2%) and 32 (14.0%) results were classified or categorized incorrectly when arm span and estimated height were substituted respectively, for actual height, with a kappa estimate of agreement 0.779 and 0.808, respectively; 17.4% and 11.0% normal results were classified, respectively, as restrictive defects using arm span and estimated height. Limits of agreement, which were almost equally wide for both sets of data, were more than the permissible intraindividual variability for FVC and FEV1. Conclusions: The substitution of arm span for height introduces statistically significant changes in spirometry results. Use of height estimated from arm span using fixed ratio also leads to misclassification of data, though less than that caused by use of arm span alone. Height estimated from arm span can be substituted for actual height in patients in whom height cannot be measured reliably. Where racial/ethnic norms for height and arm spall correlation are not available, arm span is a reasonable surrogate for standing height.