Serum osteocalcin and bone and liver alkaline phosphatase isoforms in healthy children and adolescents

We report reference values for osteocalcin and bone and liver alkaline phosphatase (ALP) isoforms in serum from 114 healthy children and adolescents, age 7-16 y. The bone and liver ALP isoforms were measured by high performance liquid chromatography (HPLC). Six ALP isoforms were separated and quantified in all samples: one bone/intestinal (B/I), two bone (B1 and B2), and three liver ALP isoforms (L1, L2, and L3). It is especially important to make distinctions between ages and gender during puberty in the interpretation of biochemical markers of bone. We observed that girls reached adult levels for osteocalcin, total ALP, and bone ALP isoforms, B/I, B1, and B2, earlier than boys. Girls in the oldest age group (15-16 y) and in the pubertal stage groups IV-V, reached higher levels than boys for the calculated ratio B1/B2 due to a more rapid decline of B2 compared with B1. This observation might indicate that B2, to a higher extent than the B1 isoform, represent a more mature expression of osteoblast differentiation during matrix mineralization in growing bone. Serial measurements of these new bone ALP isoforms could provide new insights into bone and mineral metabolism.