Reference ranges for assessment of unilateral lymphedema in legs by bioelectrical impedance spectroscopy

Background: Secondary unilateral lymphedema in the leg may occur as a consequence of pelvic surgery and/or radiation therapy, which causes damage to the pelvic lymphatic system. To date, assessment has been typically by manual measurement of the volume excess of the affected leg compared to the contralateral leg. In contrast, the assessment of unilateral arm lymphedema is readily accomplished by the use of bioelectrical impedance spectroscopy (BIS) as an increased inter-arm impedance ratio due to the presence of excess lymph in the affected arm relative to that of the unaffected arm. The presence of lymphedema is defined by a value of this ratio greater than the mean ratio plus three standard deviations (SD) observed in a comparable healthy population. The aim of the present study was to determine the equivalent reference range of the impedance ratio for the legs. This would allow a cut-off value to be established as a criterion for the detection and assessment of lower limb lymphedema. Methods: The impedances of the legs of 172 healthy females and 150 healthy males, measured by BIS, were extracted from an accumulated database of impedance data. These data were used to determine the normal distribution of inter-leg impedance ratios and the reference range and threshold value (mean + 3 SD). Results: The presence of lymphedema is indicated when the impedance ratio exceeds 1.167 in males and 1.136 in females. Unlike in the arms, the effect of limb dominance in the legs is minimal and it is suggested that no correction for limb dominance is warranted. Conclusions: The impedance ratio thresholds for lymphedema of the legs have been established, opening the way for BIS to become established clinically for the early detection and assessment of lower limb lymphedema.