Standard values of rapid turnover proteins and zinc in Japanese children

Measurement of rapid-turnover proteins has an established place in nutrition assessment and is partly dependent on the zinc metallo-enzymes involved. We investigated the reference values of rapid turnover proteins and zinc in Japanese children. This cross-sectional study was conducted at a single center. We collected data from children aged 0 to 12 years with inguinal hernia, umbilical hernia, or hydrocele of the spermatic cord, who had body mass index z scores of -2 to 2. The standard references (mean±2 SD) of transthyretin were 11.5-21.5 mg/dL in infants (≤1.5 years), 13.6-21.5 mg/dL in preschool children (1.6-6 years), and 12.3-23.4 mg/dL in preadolescent children (6.1-12 years). The standard references of retinol binding protein were 1.27-2.55 mg/dL, 1.28-2.54 mg/dL, and 1.27-2.44 mg/dL in each age group, respectively. Rapid turnover proteins did not differ significantly in each group. The transthyretin level was weakly correlated with aging (r=0.284, p=0.003) and estimated lean body mass (r=0.274, p=0.004). Retinol-binding protein was not correlated with aging and anthropometric parameters. We established reference values for rapid turnover proteins with known zinc status in Japanese children. These values were not, or only weakly, correlated with anthropometric parameters for assessing protein energy malnutrition.