Serum levels of carboxyterminal propeptide of type I procollagen in healthy children from 1 st year of life to adulthood and in metabolic bone diseases

Type I collagen is the major component of bone matrix; circulating carboxyterminal propeptide of type I procollagen (P-I-CP) levels reflect type I collagen synthesis in tissues and may be an useful index to investigate bone metabolism. We measured P-I-CP by a new radioimmunoassay in 300 healthy children and adolescents and in 40 healthy adults to provide reference data for P-I-CP values. In addition, 79 patients with diagnosed disorders of phospho-calcium metabolism (rickets, vitamin D deficient and vitamin D resistant, hyperparathyroidism, hypo- and pseudo-hypoparathyroidism, osteopenia) were evaluated. In the healthy subjects, serum P-I-CP values were higher in children than in adults; variations of P-I-CP levels were observed according to age and sexual maturation: higher values were found in the first years of life and during pubertal development; pubertal increase reflects the different timing of pubertal development in the two sexes. P-I-CP levels were increased in primary hyperparathyroidism and reduced in diseases related to impaired secretion or action of parathyroid hormone. Higher P-I-CP levels were found in vitamin D deficient and vitamin D resistant rickets. P-I-CP was reduced in anorexia nervosa and during chronic glucocorticoid treatment while it was increased in thyrotoxic osteoporosis. In idiopathic juvenile osteoporosis, P-I-CP values ranged from reduced to increased values. We conclude that P-I-CP may represent an additional biochemical marker of bone metabolism. Since age-related variations are present, reference data for the various ages are need for clinical application of this assay.