Acid-Labile Subunit in Growth Hormone Excess and Deficiency in Adults: Evaluation of Its Diagnostic Value in Comparison with Insulin-Like Growth Factor (IGF)-I and IGF-Binding Protein-3

Abstract

In serum, insulin-like growth factors (IGFs) are primarily present as a ∼150 kDa ternary protein complex, which consists of IGFs, IGF binding protein-3 (IGFBP-3), and acid-labile subunit (ALS). Like IGF-I and IGFBP-3, serum levels of ALS depend on growth hormone (GH). To date, the diagnostic relevance of ALS in adult GH deficiency (GHD) has remained uncertain. To clarify the clinical utility of ALS measurement in adults, we measured serum ALS levels in patients with adult GHD or acromegaly. We also measured the levels of serum IGF-I and IGFBP-3 in these patients to compare the utility of ALS with IGF-I and IGFBP-3 as a marker of GH secretion. Serum ALS was measured by radioimmunoassay (RIA) kit, and serum IGF-I and IGFBP-3 were measured by immunoradiometric assay (IRMA) kits in 56 patients with adult GHD (adult-onset (AO)/child-onset (CO), 13/43) and 43 patients with acromegaly. Serum ALS levels were less than 5^th percentile in 40 of 56 (71%) patients with adult GHD (32/43 (74%) for CO and 8/13 (62%) for AO), and more than 95^th percentile in 38 of 43 (88%) patients with acromegaly, respectively. Serum IGF-I levels were less than -1.96 SD in 43 of 56 (77%) patients with adult GHD (35/43 (81%) for CO and 8/13 (62%) for AO) and more than +1.96 SD in 42 of 43 (98%) patients with acromegaly, respectively. Serum IGFBP-3 levels were less than -1.96 SD in 51 of 56 (91%) patients with adult GHD (42/43 (98%) for CO and 9/13 (69%) for AO) and more than +1.96 SD in 31 of 43 (72%) patients with acromegaly, respectively. These data suggested that measurement of ALS offers no advantage over measurements of serum IGF-I and IGFBP-3. Furthermore, our results indicate that serum IGFBP-3 is the most suitable marker of GH secretion for adult GHD, especially CO, while IGF-I may be the most useful in acromegaly.