Estimating total body water in children on the basis of height and weight: a reevaluation of the formulas of Mellits and Cheek.

An estimate of total body water (TBW) has important implications in clinical practice. For patients on peritoneal dialysis (PD), the estimate is critical when determining the delivered dialysis dose. The formulas of Mellits and Cheek have been recommended to estimate TBW in children on PD. These formulas were derived from healthy children, and very few infants were included. To assess the accuracy of these formulas, the original data were obtained and additional data from a broad literature review were compiled. The majority of the new data points were in the infant age range. Data were fitted using least-squares methodology and backward elimination to obtain a parsimonious model. Best fits were obtained using age, gender, and weight or a height x weight term. The results of the curves are as follows: Infants 0 to 3 mo (n= 71): TBW = 0.887 x (Wt)(0.83) Children 3 mo to 13 yr(n = 167): TBW = 0.0846 x 0.95([if female]) x (Ht xWt)(0.65) Children > 13 yr (n = 99): TBW = 0.0758 x 0.84([if female]) x (Ht x Wt)(0.69) When compared with the previous Mellits and Cheek formulas, the new formula fits better for infants (comparison of prediction errors, P < 0.0004). These newer formulas do not perform significantly better for the older two groups. Actual TBW measurement in children on PD must still be determined to verify the use of these formulas and to accurately assess dialysis delivery and adequacy.