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Influence of Demographic Factors and Sport Type on Growth Hormone-Responsive Markers in Elite Athletes

Garvan Institute of Medical Research and Department of Endocrinology (A.E.N., T.V.N., K.-C.L., K.K.H.), Darlinghurst, New South Wales 2010, Australia; Australian Sports Drug Testing Laboratory (C.J.H., G.J.T., R.K.), National Measurement Institute, Pymble, New South Wales 2073, Australia; ANZAC Research Institute (M.J.S., D.J.H.), Concord Hospital, University of Sydney, Sydney, New South Wales 2139, Australia; and Kolling Institute of Medical Research (R.C.B.), University of Sydney, Royal North Shore Hospital, St Leonards, New South Wales 2065, Australia

Address all correspondence and requests for reprints to: Professor K. K. Ho, Pituitary Research Unit, Garvan Institute of Medical Research, 384 Victoria Street, Darlinghurst 2010, Australia. E-mail: K.Ho{at}garvan.org.au.

Context: GH-responsive markers of the IGF system and of collagen turnover hold promise as the basis of a GH doping test.

Objective: The purpose of this study was to determine the influence of age, gender, body mass index (BMI), ethnicity, and sporting type on GH-responsive serum markers in a large cohort of elite athletes from different ethnic backgrounds.

Design: The study was designed as a cross-sectional study.

Participants: A total of 1103 elite athletes (699 males, 404 females), aged 22.2 ± 5.2 yr, from 12 countries and 10 major sporting categories participated in this study.

Main Outcome Measures: Serum IGF-I, IGF binding protein-3 (IGFBP-3), acid labile subunit (ALS), and collagen markers [N-terminal propeptide of type I procollagen (PINP), C-terminal telopeptide of type I collagen (ICTP), N-terminal propeptide of type III procollagen (PIIINP)] were measured.

Results: There was a significant negative correlation (r = –0.14 to –0.58, P < 0.0005) between age and each of the GH-responsive markers. Serum IGF-I, IGFBP-3, and ALS were all lower (P < 0.05), whereas the collagen markers PINP, ICTP, and PIIINP were higher (P < 0.05) in men than in women. Multiple regression analysis indicated that age, gender, BMI, and ethnicity accounted for 23–54% of total between-subject variability of the markers. Age and gender cumulatively accounted for 91% of the attributable variation of IGF-I and more than 80% for PINP, ICTP, and PIIINP. Gender exerted the greatest effect on ALS (48%), and BMI accounted for less than 12% attributable variation for all markers. The influence of ethnicity was greatest for IGFBP-3 and ALS; however, for the other markers, it accounted for less than 6% attributable variation. Analysis of 995 athletes indicated that sporting type contributed 5–19% of attributable variation.

Conclusions: Age and gender were major determinants of variability of GH-responsive markers except for IGFBP-3 and ALS. Ethnicity is unlikely to confound the validity of a GH doping test based on IGF-I and these collagen markers.

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