Height velocity is difficult to assess because growth is very slow. Current practice of calculating it from measurements taken at several month intervals is insufficient for managing children with growth disorders. We identified a bone growth by-product (Collagen X bioMarker, CXM) in blood that in preliminary analysis in healthy children correlated strongly with conventionally determined height velocity and displayed a pattern resembling published norms for height velocity vs age.The goal was to confirm our initial observations supporting the utility of CXM as a height velocity biomarker in a larger number of subjects and establish working reference ranges for future studies.CXM was assessed in archived blood samples from 302 healthy children and 10 healthy adults yielding 961 CXM measurements. 432 measurements were plotted by age, and sex-specific reference ranges were calculated. Serial values from 110 subjects were plotted against observed height velocity. Matched plasma, serum, and dried blood spot readings were compared.Correlation of blood CXM with conventional height velocity was confirmed. Scatter plots of CXM vs age showed a similar pattern to current height velocity norms, and CXM levels demarcated the pubertal growth spurt in both girls and boys. CXM levels differed little in matched serum, plasma and dried blood spot samples.Blood CXM offers potential means to estimate height velocity in real-time. Our results establish sex-specific, working reference ranges for assessing skeletal growth, especially over time. CXM stability in stored samples makes it well suited for retrospective studies.