Obtaining spirometric reference values when height is not available – comparison of alternative anthropometric measures

Abstract

Introduction: Height is one of the variables used to derive reference values for respiratory function but it is not always available. To fulfil this need, different formulas are described in literature. Aim: To understand which method best estimate height in order to obtain Forced Vital Capacity (FVC) and Forced Expiratory Volume in 1st second (FEV1) reference values. Methods: The true stature (TS) and five alternative anthropometric measures that estimate height [arm span using a regression equation (ASR), arm span using a fix correction factor (ASF), half arm span, knee height and ulnar length] were measured for all patients. To assess the differences between the TS versus the estimated heights and the respective reference values of FVC and FEV1, T Student Test and Wilcoxon test were used. Agreement was evaluated by Intraclass Correlation Coefficient and by Bland-Altman plot. Results: A total of 160 subjects were recruited but 14 patients were excluded due to skeletal deformities. The predicted FVC and FEV1 using all alternative anthropometric measures were statistically different from those calculated by TS, except for ASF. The limits of agreement were wide for all alternative measures. With the exception of ASF, predicted FVC and FEV1 were overestimated when using all other alternative measures. Conclusions: For the purpose of replacing height in order to obtain predicted values of FVC and FEV1, the ASF was shown to be the most accurate and recommendable method. However, we must be aware there is a possible degree of error.

Keywords

• Spirometry
• Anthropometry
• Respiratory function tests