Objectives: The aims of this study were to validate the use of filter paper to measure insulin-like growth factor-I (IGF-I) and to establish normal levels of IGF-I in children appearing healthy, from birth to 5 years of age in an African population.
Methods: We determined IGF-I from blood collected on filter paper. We validated this method by comparing the IGF-I values from dried blood spots on filter paper (kept at 4 degrees C and ambient temperature) and from serum among 13 children under 5. IGF-I were measured by the classical IGF-I RIA, after separation of the IGF-I from its binding proteins, using Sep-Pak chromatography. To establish normal levels of IGF-I, we conducted a cross-sectional study and collected blood samples with filter paper among 360 children in Ouagadougou (Burkina Faso).
Results: IGF-I determined from dried blood spots on filter paper were in good agreement with IGF-I levels obtained from blood serum, whether the filter papers were kept at 4 degrees C or at ambient temperature. The results of IGF-I-levels in apparently healthy children showed that geometric mean IGF-I ranged from 27 microg/l in boys younger than five months to 31 microg/l in 5-year-old boys. In girls, mean IGF-I ranged from 29 microg/l for girls younger than five months to 45 microg/l at the age of 5. From birth to 24 months, IGF-I decreased by 0.32+/-0.08 microg/l/month in boys and by 0.27+/-0.06 microg/l/month in girls and these decreases were not significantly different (p=0.95). After the age of 24 months, there was an increase in IGF-I of 4.9+/-1.3 microg/l/year in boys and of 8.4+/-0.8 microg/l/year in girls. This increase was indeed significantly different (p<0.001).
Conclusions: Reference values of IGF-I for African boys and girls were determined. They will be used for endocrine evaluations and nutritional monitoring.