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

Insulin-like growth factors (IGFs) and IGF binding proteins (IGFBPs) play a n important role in cell growth and differentiation. Clinical and epidemiol ogical studies have indicated that measuring IGFs and IGFBPs in blood has p otential implications in assessing growth-related abnormalities and risks o f certain types of cancer. To facilitate the application, we reported a lar ge collection of reference ranges of IGFs and IGFBPs in normal population a nd 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 we re low at birth and increased with age through puberty. After puberty the l evels declined slowly with age. Overall, IGF-I, IGFBP-3 and ALS were slight ly higher in females than in males. Free IGF-I accounted for about 1% of th e 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 stab le after puberty. There was little difference in IGF-II levels between gend ers. IGFBP-2 levels declined with age from birth to puberty. Levels of IGFB P-6 in contrast were increased with age. These IGF binding proteins were hi gher in males than in females. IGFs, IGFBP-3 and ALS were 5-10% higher in s erum than in plasma. IGFBP-2 and IGFBP-6 differed substantially between ser um 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. Cl in. Lab. Anal. 13:166-172, 1999. (C) 1999 Wiley-Liss, Inc.