Objective: Bioelectrical impedance vectorial analysis (BIVA) can be considered a favorable method for evaluation and monitoring of nutritional and hydration status without assumptions regarding body composition or requirement of prediction formulas. The present study aimed to determine bivariate tolerance intervals of the whole-body impedance vector for healthy term infants aged 1 to 3 months.
Methods: This is a descriptive cross-sectional study. Anthropometric and bioelectrical impedance data (800 mA-50 kHz) were obtained. Bivariate vector analysis was conducted with the resistance-reactance (RXc) graph method. BIVA software was used to construct the graphs.
Results: A total of 150 appropriate for gestational age infants (48.7% boys) who were exclusively breastfed and were 56.4 (SD = 23.1) days of age were studied. RXc tolerance ellipses (50, 75, and 95%) were constructed for boys and girls, but a general reference graph was defined for all infants considering the overlapping of ellipses between the genders. All graphs differed from those in national and foreign studies.
Conclusion: New reference tolerance ellipses (95, 75, and 50%) for 1- to 3-month-old infants were constructed, pointing out the need for specific reference values of total body impedance vectors in different regions of Brazil. The RXc tolerance ellipses can be used for clinical practice and provide an easy method to evaluate and monitor body composition and hydration status.
Keywords: Body composition; bioelectrical impedance vector analysis; infants; nutritional assessment; phase angle.