Reference equations for predicting standing height of children by using arm span or forearm length as an index

Standing height (SH) is the most reliable parameter used to predict spirometric values in children, but measurement of this parameter may be difficult in children with thoracic or spinal abnormalities. This study was designed to establish reference equations to estimate SHs of children using their arm span length (ASL) or forearm ulnar length (UL) as an index.

Children aged 1-17 years were enrolled to measure their SH, body weight, ASL, and UL. Sex and age were also recorded. The relationship between SH and children's weight, age, ASL, and UL were analyzed. Regression equations using different indexes for SH of enrolled cases were used, and adults aged 18-64 years were also enrolled for comparison.

A total of 512 children and 144 adults were enrolled. There was a strong linear relationship between SH and both ASL and UL in children and adults. Pearson's correlation coefficients of SH for ASL and UL were 0.989 and 0.968 (p < 0.001) in children and 0.933 and 0.845 (p < 0.001) in adults. The linear regression equations for estimating SH in children were calculated as SH = 9.363 + 0.943 ASL (r² = 0.978, p < 0.001) and SH = 14.542 + 5.570 UL (r² = 0.936, p < 0.001). In adults, age and sex were also added as indexes: SH = 59.849 + 0.642 ASL-0.047 Age +3.431 Sex (male = 1; female = 0) (r² = 0.887, p < 0.001) and SH = 102.824 + 2.317 UL -0.049 age + 6.739 sex (r² = 0.773, p < 0.001).

Both ASL and UL have a significant linear relationship with SHs of children and adults. True SH can be estimated using regression equations with ASL or UL as a single index for situations where direct measurement of SH is difficult.