Objectives: To study the relative roles of androgens and the growth hormone-insulin-like growth factor I (GH-IGF-I) system in the regulation of erythropoiesis in boys during puberty.Study design: We treated 23 boys with constitutional delay of puberty with low-dose testosterone (T), in combination with either a potent aromatase inhibitor, letrozole (Lz; 2.5 mg/d), or placebo (P).The study design was randomized, doubleblinded, and placebo-controlled between the treated groups.Treatment with T +Lz was associated with high T and low IGF-I concentrations, whereas treatment with T +P resulted in moderately increased T and high IGF-I concentrations.Results: The blood hemoglobin concentration increased by 1.6 g/dL in T +Lz-treated boys, despite their low IGF-I concentrations.The estimated red blood cell volume increased more in T +Lztreated than in T +P-treated boys (349 vs 174 mL, respectively, P =.01).Serum T concentrations during the treatment period correlated with the 12-month increments in hemoglobin and red blood cell volume.The changes in blood hemoglobin concentration and RBC in T +Lz-treated boys were similar to those we observed in a population of normal adolescent boys in the late stages of puberty.Conclusions: The pubertal increase in hemoglobin concentration in boys is related to direct androgen effects.
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