Validity of bioelectrical impedance analysis to assess fat-free mass in patients with head and neck cancer: an exploratory study.
BACKGROUND
The purpose of this study was to validate bioelectrical impedance analysis (BIA) using the Geneva equation for fat-free mass (FFM) in patients with head and neck cancer.


METHODS
In 24 patients with head and neck cancer, agreement between BIA (FFMBIA ) and dual energy x-ray absorptiometry (FFMDXA ) 1 week before (T0 ), 1 month (T1 ), and 4 months (T2 ) after cancer treatment was analyzed.


RESULTS
FFMBIA did not differ from FFMDXA (mean difference 0.71 ± 1.9, 0.30 ± 1.9, and 0.02 ± 2.1 kg) at any time point. Only at T0 , mean FFM correlated to the difference between FFMDXA and FFMBIA (r = 0.48; p = .017). Limits of agreement were 3.8, 3.7, and 4.1 kg, respectively. Concordance Correlation Coefficients were 0.98 at all time points.


CONCLUSION
BIA may be used to assess FFM with reasonable validity based on mean-level comparisons, but differences between BIA and DXA may vary by about 4 kg in an individual patient. These results require confirmation in a larger sample of patients with head and neck cancer.