Diurnal rhythm of serum osteocalcin in normal children

The aim of the present study was to assess diurnal levels of serum osteocalcin in normal children using a recently introduced fluoroimmunoassay (Pharmacia Osteocalcin CAP FEIA) measuring solely the intact peptide. Five girls and two boys aged 10.4-13.6 (mean 12.2) y were studied. Blood samples for determination of osteocalcin were collected every 2h throughout the day. A statistically significant rise in serum osteocalcin (F = 6.7, p < 0.001) with a peak at 08.00 h and a nadir lasting from 10.00 to 24.00 h was found. Trough and peak levels (at 16.00 and 08.00 h, respectively) were 41.6 +/- 6.8 and 66.0 +/- 10.5 microg l(-1) (mean +/- SEM). The circadian variation should be taken into consideration when single assessments of serum osteocalcin in children are performed.