Reference Values for Interstitial Tissue Water in the Head and Neck Area: Non-lymphedema Participants

<b><i>Background:</i></b> To determine reference values for interstitial percentage water content (PWC) in the head and neck area, in a large and heterogeneous sample of non-lymphedema participants; to determine left-right interchangeability of measurement locations, and to explore to what extent PWC values vary with age, sex, skin type, and body mass index (BMI) at the determined measuring locations. <b><i>Methods and Results:</i></b> In this cross-sectional study, a heterogeneous group of adult non-lymphedema participants was included. PWC was measured according to an earlier developed protocol by seven trained health professionals. Limits of agreement, error correlations, and bias, as determined by Bland and Altman analysis, were used to assess the left-right interchangeability. Mixed effects models were used to explore variables that explain the variety in PWC values. Stratified descriptive reference values were calculated for relevant subgroups. A total of 412 participants were included in the study. The unstratified PWC values ranged from 38.9% to 45.5%. Sex and BMI were statistically significantly correlated with PWC values, while sex is also clinically relevant. <b><i>Conclusion:</i></b> This study resulted in sex-stratified reliable reference PWC values in the head and neck area for healthy adults. A difference of 10 percentage point between the same measurement point on the left and right side of the head or neck can be considered normal. The established reference values for PWC can be used to assist diagnosis and follow-up in patients with lymphedema in the head and neck area.