[Hydroxyproline in morning urine. A reliable parameter for bone turnover in childhood].

OH-P/Cr was measured in morning fasting urine specimens of 300 healthy subjects and of children with disorders of calcium metabolism receiving no diet. In healthy children the values were sex and age dependent reflecting the different height velocities. The OH-P excretion was not different in schoolchildren receiving a OH-P-poor diet for at least two days in comparison to subjects of the same age group with unrestricted diet. OH-P/Cr correlated well with serum alkaline phosphatase (AP) activity and decreased rapidly after a calcium load. OH-P/Cr and AP were elevated in patients with increased bone turnover (hyperparathyroidism and hypophosphatemic rickets). In contrast, the OH-P excretion was normal in children with permanent or transient isolated hyperphosphatasemia. In children with vitamin D deficiency rickets there was a further increase of OH-P/Cr in response to vitamin therapy, while the AP activity, which reflects osteoblastic activity, tended to fall. This indicates that the observed increment of the OH-P excretion in these children is due to a temporary resorption of osteoid caused by the increasing levels of vitamin D metabolites. It is concluded that the measurement of OH-P/Cr provides a useful tool of bone turnover in children, in that it makes complete 24 h-urine collections and a OH-P free diet unnecessary. In combination with other indices of calcium metabolism the determination of the OH-P ratio is considered to be a valuable measure for the diagnosis and follow-up of bone disorders.(ABSTRACT TRUNCATED AT 250 WORDS)