Insulin-like growth factors (IGF-I, free IGF-I, and IGF-II) and insulin-like growth factor binding proteins (IGFBP-2, IGFBP-3, IGFBP-6, and ALS) in blood circulation

Abstract

Insulin‐like growth factors (IGFs) and IGF binding proteins (IGFBPs) play an important role in cell growth and differentiation. Clinical and epidemiological studies have indicated that measuring IGFs and IGFBPs in blood has potential implications in assessing growth‐related abnormalities and risks of certain types of cancer. To facilitate the application, we reported a large collection of reference ranges of IGFs and IGFBPs in normal population and evaluations of these molecules in serum and plasma as well as the impact of freeze‐thaw cycles on the measurement. IGF‐I, IGFBP‐3 and ALS showed a similar pattern of change associated with age. Levels of these molecules were low at birth and increased with age through puberty. After puberty the levels declined slowly with age. Overall, IGF‐I, IGFBP‐3 and ALS were slightly higher in females than in males. Free IGF‐I accounted for about 1% of the total IGF‐I and its variation with age was similar to total IGF‐I. IGF‐II levels were also increased with age from birth to puberty, but became stable after puberty. There was little difference in IGF‐II levels between genders. IGFBP‐2 levels declined with age from birth to puberty. Levels of IGFBP‐6 in contrast were increased with age. These IGF binding proteins were higher in males than in females. IGFs, IGFBP‐3 and ALS were 5‐10% higher in serum than in plasma. IGFBP‐2 and IGFBP‐6 differed substantially between serum and plasma. Freeze‐thaw treatment up to five cycles had little impact on plasma levels of IGFs and IGFBP‐3. Our observations suggest that levels of IGFs and their binding proteins are varied with age, gender, and types of specimen and that these variations need to be taken into consideration when IGFs and their binding proteins are utilized in clinic and research. J. Clin. Lab. Anal. 13:166–172, 1999. © 1999 Wiley‐Liss, Inc.

Associations between plasma insulin-like growth factor-I and the markers of inflammation interleukin 6, C-reactive protein and YKL-40 in an elderly background population

“…We have compared measurements of IGF-I in plasma and serum in a separate series of 35 individuals. IGF-I levels were on average 22% higher in serum than in plasma, independent of the IGF-I level, which is in agreement with a previous report [18].…”

A cross-sectional analysis of the association between diet and insulin-like growth factor (IGF)-I, IGF-II, IGF-binding protein (IGFBP)-2, and IGFBP-3 in men in the United Kingdom

“…Only prolonged fasting over several days has any impact on circulating IGF or IGFBP levels (apart from IGFBP-1, which was not measured) [12]. Samples underwent two freeze-thaw cycles prior to IGF assay, shown to have no effect on IGFs or IGFBP-3 levels [23]. IGF-I, IGF-II, and IGFBP-3 assays were carried out using an in-house radioimmunoassay (RIA) in a single local laboratory by staff blinded to FFQ data.…”

Utility of Free IGF-I Measurements

“…In adults with GHD, the measurement of serum total IGF-I appears to be of even less diagnostic usefulness, in particular in those patients with adult-onset GHD, who for some yet unsolved reason Pituitary (2007) 10:181-187 183 appear to have higher serum total IGF-I levels than agematched patients with childhood-onset GHD [31]. The IGFBP-3 and ALS have also been examined as markers of GHD, but generally both peptides are of less diagnostic usefulness than total IGF-I and at best they may be considered as additional GH-markers rather than substitutes for IGF-I [32][33][34]. Therefore, with the introduction of free IGF-I assays, much enthusiasm was put into testing this parameter as a diagnostic marker of GHD.…”