Reference ranges for serum β-trace protein in neonates and children younger than 1 year of age

Background: beta-Trace protein (BTP) has been proposed as an alternative endogenous marker of glomerular filtration rate. Data on BTP reference ranges in young children are scarce. We therefore aim to establish reference ranges and examine the developmental course of serum BTP in basically healthy children younger than 1 year of age. Methods: Single blood samples were taken from healthy children (born at gestational age >= 37 weeks) <12 months of age. Serum BTP was measured using the N latex B-trace protein assay (Siemens Diagnostics, Deerfield, IL, USA) on an Immage (R) 800 Rate Nephelometer (Beckman Coulter Inc. Brea, CA, USA). Serum creatinine and cystatin C were additionally determined and compared to reference values to confirm a normal renal function. Results: From June 2010 to January 2014, 95 blood samples were collected from 95 children {67.4% male; median age 120 days [inter quartile range 57-166]}. BTP was normally distributed (mean concentration 0.84 +/- standard deviation 0.35 mg/L). Considering all children, the 50th centile BTP reference concentration was 0.82 mg/L (5th-95th centiles; 0.27-1.38). BTP concentrations were the highest in neonates and steadily declined with increasing age (Spearman's rank correlation was -0.415, p=0.002). No gender differences were found. Conclusions: Our data provide a BTP reference range for the first year of life. Seeing the biological pattern of BTP, with only a limited postnatal decline, this marker might offer a promising alternative to serum creatinine-based methods for estimating glomerular filtration rate in newborns.