Impedance of Extracellular Fluid, Volume, and Local Tissue Water Can Be Reliably Measured in People With Lower Limb Lymphedema

OBJECTIVE: Lower limb lymphedema (LLL) is a chronic condition. To be able to evaluate changes of LLL over time and effects of interventions, reliable measurement methods are important. Currently, there is limited knowledge of the reliability of commonly used measurement methods in LLL. The study objective was to evaluate the test–retest (intrarater) reliability of impedance of extracellular fluid, volume, and local tissue water measurements in people with unilateral or bilateral LLL and measurement errors both for a group of people and for a single individual. METHODS: Forty-two people with mild to moderate unilateral or bilateral, primary or secondary LLL were measured twice, 2 weeks apart. Impedance of extracellular fluid was measured by bioimpedance spectroscopy and calculated as arm-to-leg ratio, volume with circumference measurements every 4 cm, and local tissue water with tissue dielectric constant at 14 points. Test–retest reliability was evaluated using the intraclass correlation coefficient [ICC(2,1)], changes in the mean, SE of measurement in relative terms (SEM%), and the smallest real difference in relative terms (SRD%). RESULTS: For the impedance ratio, the reliability was high [ICC(2,1) = 0.79–0.90] and the measurement errors were acceptable (SEM% = 5.0%–5.2%; SRD% = 14.0%–14.4%). For volume, the reliability was high (ICC = 0.99) and the measurement errors were low (SEM% = 1.1%–1.7%; SRD% = 3.1%–4.6%). For the tissue dielectric constant, the reliability was fair to excellent [ICC(2,1) = 0.68–0.96] and the measurement errors were acceptable (SEM% = 4.2%–9.7%; SRD% = 11.7%–26.8%). CONCLUSIONS: Measurements of impedance of extracellular fluid, volume, and local tissue water are reliable in people with mild to moderate LLL. The measurement errors were acceptable in all 3 methods indicating that real, clinical changes in lymphedema can be measured both for a group of people and a single individual. IMPACT: The results from this test–retest reliability study can help clinicians and researchers to interpret if real clinical changes in lymphedema occur over time or after an intervention in people with mild to moderate LLL.