C H A P T E R 3 predictive value: 90%). On the other hand they were indistinguishable from each other when TBW was < 0.7 l/m2 (Figure 2 quadrant C and D, negative predictive value: 32%). Based on these results, the change in TBW < 0.7 l/m2 in SGA children is not a tool to decide to stop treatment with rhGH treatment, but a change in TBW > 0,7 l/m2 is highly predictable for a good response to therapy. In this study different results are seen between GHD children and children born SGA. GHD children show a lower FFM/ heigt2 and thereby a higher fat mass (FM) before start of any treatment, compared to SGA children who show a higher FFM/heigt2 4,5. The treatment with rhGH causes a shift in body composition to-‐ wards the FFM in GHD children, possibly because their amount of fat deposit is much higher than in SGA children. Another possible explanation could be that SGA children do not have a growth hormone deficiency. The effect of rhGH treatment is therefore less obvious than in GDH children. Also a possible metabolic factor could be involved. One of the factors mentioned with respect to the stunted growth of SGA children is reduced sensitivity for IGF-‐1 (insulin-‐like growth factor 1)20. IGF-‐1 is mainly secreted by the liver as a result of stimulation by growth hormone. IGF-‐1 expression is required for achieving maxi-‐ mal growth. Short SGA children show plasma IGF-‐1 levels that are in the lower normal range21. The above mentioned factors could possibly explain why SGA children show less increase of TBW/height2 as response to treatment, despite their increase in height. In SGA children this shift can be seen less obvious. Other methods for measuring body composition in GHD or SGA children are evalu-‐ ating the change in body mass index (BMI) or evaluating the change in weight for height (SDS) after one year of treatment. In the study of Ernst et al.22 is found that the mean change in BMI (kg/m2) after 1 year of rhGH treatment is -‐0,04 kg/m2. The mean change in weight for height (SDS), after 1 year of rhGH treatment is 0,11. Apparently, BMI and weight for height of SGA children barely change during the first year of rhGH treatment. Therefore, the TBW method is much more appropriate than the other described methods. Another method of measuring TBW is the un-‐ derwater weighting. This method is not practically achievable and is not used in this study. Changes in TBW under influence of rhGH treatment are also dependent on other factors like age, sexe and diet. These are determinants of TBW23. 52
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