Plasma insulin-like growth factor-1 (IGF-1) in the diagnosis of acromegaly

Abstract

Insulin-like growth factor-1 (IGF-1} has been suggested to be a good alternative marker for the diagnosis of acromegaly. In this study, 42 samples collected from 25 treated acromegalic patients over 2 years were assayed for fasting growth hormone (CH), IGF-1 and IGF-binding protein-3 (IGFBP-3). 23/42 (54.8%) samples were considered normal based on the normal cut-off value of 10 mlU/L for random GH secretion, but only 9 (21.4%) and 16 (38.1 %) samples were within the age-matched reference values for IGF-1 and IGFBP-3 respectively. Three patients had persistently elevated levels of GH, IGF-1 and IGFBP-3, while 2 patients were diagnosed biochemically cured when these markers remained normal up to 8 months. IGF-1 remained high in 2 other patients despite normalised GH and IGFBP-3, and disease activity subsequently returned when IGFBP-3 also became elevated. Similarly, 2 patients diagnosed normal following OGTT also had high IGF-1, and subsequently, showed increased secretions of GH and IGFBP-3. IGF-1 has a curvilinear relationship with GH,plateauing at higher GH levels. Failure to recognise this relationship caused many investigators to doubt the usefulness of IGP-1. Nevertheless, this study has shown that IGF-1 is indeed a reliable prognostic index for acromegaly, provided results are interpreted with reference to well established, age-matched normal values.