Serum
insulin-like growth factor-1 (IGF-1) is a sensitive marker of
growth hormone (GH) activity. The levels of
IGF-1 vary widely, peaking during puberty and declining with advancing age. During adolescence, serum
IGF-1 levels tend to correlate better with pubertal stage rather than chronological age. Here we discuss two cases of
delayed puberty, both in their 20s, who presented with high serum
IGF-1 but no clinical or biochemical evidence of hypersomatotropism as confirmed by appropriate GH response to an oral
glucose challenge. Both individuals achieved full pubertal status with
testosterone replacement
therapy and their serum
IGF-1 levels settled into normal age-specific range. We suggest that in chronologically adult individuals with
delayed puberty, serum
IGF-1 should not be interpreted on the basis of age-specific normal values but rather on their pubertal status. Furthermore, in the absence of another cause of elevated
IGF-1, the expectation is that
IGF-1 levels will decline towards age-normative ranges following
androgen replacement
therapy.