Paediatric reference values for the C-terminal fragment of fibroblast-growth factor-23, sclerostin, bone-specific alkaline phosphatase and isoform 5b of tartrate-resistant acid phosphatase

Background: Paediatric reference values for novel markers of phosphate homeostasis, bone formation and resorption and their putative relationship to growth are lacking. Methods: A total of 424 healthy children, adolescents and young adults (221 males) aged 0.1-21 y, were enrolled in this cross-sectional study. Height, weight and height velocity were assessed. Plasma/serum samples for determination of C-terminal fragment of fibroblast growth factor-23 (cFGF-23), sclerostin, bone alkaline phosphatase (BAP) and tartrate-resistant acid phosphatase 5b (TRAP5b) were available from 222, 264, 352 and 338 individuals, respectively. Calculation of cross-sectional centiles and z-scores was based on median (M), standard coefficient of variation (S) and the Box-Cox power (L) of transformation (LMS method) per age cohort. Correlations between variables as well as with growth were assessed. Results: cFGF-23, BAP and TRAP5b were significantly correlated with age (each P < 0.01), with highest values during infancy and adolescence. Serum levels of BAP and TRAP5b were significantly higher in adolescent boys compared with girls (each P < 0.01). In contrast, sclerostin levels were independent of age and gender. BAP and TRAP5b were strongly correlated and both were significantly associated with cFGF-23 and sclerostin as well (each P < 0.01). cFGF-23 was positively correlated with serum phosphate and renal phosphate threshold concentration (each P < 0.01). Height, weight, body mass index and height velocity were weakly correlated with BAP and TRAP5b (each P < 0.05). Conclusions: This study provides age- and gender-related centile charts and z-scores for cFGF-23, BAP, TRAP5b and sclerostin and highlights the link between phosphate homeostasis and markers of bone metabolism during growth. Ann Clin Biochem 2012; 49: 546-553. DOI: 10.1258/acb.2012.011274