Abstract
Background Limb circumference measurements (CM) and perometry are the preferred methods for
objectively measuring arm volume in lymphedema surgery research. Understanding the
measurement bias involved in these measuring systems is important to properly interpret
and compare studies and their results.
Methods Arm volumes from 91 patients were measured using sequential girths and the truncated
cone formula (CM) and with the use of an automated perometer (perometry). The absolute
volume of the largest arm (V), the volume difference between the arms (VD), and the
relative difference between them (percentage of excess volume [PEV]) were calculated
with both methods. The agreement between methods was assessed by the Pearson's correlation
test and the Bland–Altman's method.
Results Correlations were strong for V (r = 0.99), VD (r = 88), and PEV (r = 0.86). Volumes measured by perometry were, on average, 10.6 mL smaller than volumes
calculated from CM, while their limits of agreement (LOA) ranged from −202 to 181
mL. The LOA represents the range we could expect the arm volumes measured with the
two methods to differ by chance alone, 95% of the times. For VD, LOA was −101 to 141
mL, with a mean difference of 19.9 mL, while PEV had a mean difference of 0.9%, with
LOA ranging from −5 to 6.8%.
Conclusion There is considerable measurement error between arm volume estimated by perometry
and by CM. Volumes calculated with these methods should be compared with caution.
Furthermore, we observed an increasingly relevant measurement bias in outcomes that
are mathematically derived from arm volumes.
Keywords
lymphedema - outcome - measurement error
