Validity and interobserver agreement of lower extremity local tissue water measurements in healthy women using tissue dielectric constant
Mads Radmer Jensen, MD, Department of Clinical Physiology and Nuclear Medicine, Bispebjerg Hospital, University Hospital of Copenhagen, Bispebjerg Bakke 23, 2400 Copenhagen NV, Denmark
Tissue dielectric constant (TDC) measurement may become an important tool in the clinical evaluation of chronic lower extremity swelling in women; however, several factors are known to influence TDC measurements, and comparative data on healthy lower extremities are few.
Thirty-four healthy women volunteered. Age, BMI, moisturizer use and hair removal were registered. Three blinded investigators performed TDC measurements in a randomized sequence on clearly marked locations on the foot, the ankle and the lower leg. The effective measuring depth was 2·5 mm.
The mean TDC was 37·8 ± 5·5 (mean ± SD) on the foot, 29·0 ± 3·1 on the ankle and 30·5 ± 3·9 on the lower leg. TDC was highly dependent on measuring site (P<0·001) but did not vary significantly between investigators (P = 0·127). Neither age, BMI, hair removal nor moisturizer use had any significant effect on the lower leg TDC. Intraclass correlation coefficients were 0·77 for the foot, 0·94 for the ankle and 0·94 for the lower leg.
The TDC on the foot was significantly higher compared with ankle and lower leg values. Foot measurements should be interpreted cautiously because of questionable interobserver agreement. The interobserver agreement was high on lower leg and ankle measurements. Neither age, BMI, hair removal nor moisturizer use had any significant on effect on the lower leg TDC. TDC values of 35·2 for the ankle and 38·3 for the lower leg are suggested as upper normal reference limits in women.