Relationship of somatomedin-C concentration to bone age in boys with constitutional delay of growth
K. R. Rubin, J. M. Lichtenfels, S. K. Ratzan, M. Ozonoff, D. W. Rowe and D. E. Carey
Serum somatomedin-C (Sm-C) levels increase sharply during puberty, leading
to difficulty in the interpretation of Sm-C values obtained from children
who exhibit a discrepancy between chronological age (CA) and pubertal
development. To evaluate the utility of assessing Sm-C levels on the basis
of bone age (BA), we measured serum Sm-C levels in 44 boys with
constitutional delay of growth (CDG). Levels of Sm-C were compared with the
normative data of the Nichols Institute Reference Laboratories (NIRL), Los
Angeles, by age category, substituting BA for CA. We found the mean Sm-C
level in boys with CDG to be lower than that for NIRL normal subjects in
each age category for both CA and BA, but the regression curve for Sm-C
levels based on BA more closely approximated the NIRL regression curve than
did the curve based on CA. The rise in Sm-C levels observed in NIRL normal
subjects between CA 13 to 14 years is delayed in boys with CDG until CA 15
to 17 years only when a correction for BA is not made. We conclude that in
boys with CDG, Sm-C levels should be interpreted on the basis of BA rather
than CA, especially during the peripubertal period. The observation of
blunted Sm-C levels in all age categories, even when BA was used, suggests
that short children with presumed CDG may be at high risk for a
"nonclassic" form of growth hormone deficiency.