Free deoxypyridinoline in urine and serum--results in children and adolescents.

The urinary excretion of the collagen crosslinking compound dexoypyridinoline (DPD) is considered a specific index of bone resorption. Here we report on the levels of free (i.e., non peptide-bound) DPD in the urine and serum of subjects from 5 to 19 years of age, as determined by a new radioimmunoassay. Reference values for free DPD were established using 24-h urine collections from 118 healthy children and serum samples from 133 children with acute febrile illnesses. Serum and urine levels of free DPD were compared in samples from 23 short, normal children. Additionally, total (the sum of peptide-bound and free) DPD was measured by high-performance liquid chromatography in the 24-h urine collections. Urinary-free DPD was significantly correlated with total DPD (r = 0.90; P < 0.001) and declined steadily with age. Serum levels of free DPD ranged from 0.9 to 5.7 nmol/l and varied with age in boys only. No significant association was found between serum and urine levels of free DPD (r = 0.08; P = 0.37). In conclusion, urinary-free DPD did not reflect enhanced bone turnover during the time of puberty. Free DPD serum levels are very low, which may be due to rapid clearance via the kidneys.