Background: Red blood cell (RBC) transfusions are associated with the development of retinopathy of prematurity (ROP). During the period of retinal neovascularization a rise of insulin-like growth factor 1 (IGF-1) may trigger rapid growth of new blood vessels. Objectives: To study endocrine factors in RBC transfusions that might be of importance for ROP. Methods: IGF-1, IGF-2 and their binding proteins 1–3 (IGFBP-1–3) were determined by radioimmunoassays in 7 very-low-birthweight (VLBW) infants with ROP ≧ stage 2 receiving a RBC transfusion, in 10 controls (VLBW infants with ROP ≤ stage 1, no transfusion), in supernatants of 7 RBCs and of 5 washed RBCs (WRBC). Results: IGF-1 (mean ± SD) in infants with ROP was 20.0 ± 4.2 µg/l, in controls 35.9 ± 15.2 µg/l (Mann-Whitney U test, p = 0.030). IGF-1 in RBC was 12.88 ± 5.03 µg/l and in WRBC 0.45 ± 0.74 µg/l (average of the three-course washing procedure). IGF-2 in infants with ROP was 485.67 ± 158.73 µg/l, in controls 389.9 ± 102.8 µg/l (not significant), in RBC 109.50 ± 117.89 µg/l, in WRBC 61.07 ± 30.0 µg/l. Except for IGFBP-3 other IGFBPs were barely or not detectable in RBC or WRBC. Conclusions: Considering lower IGF-1 concentrations in preterm infants than in adults (factor 20), the IGF-1 in RBC transfusions is equivalent to a single dose of 1 µg/kg IGF-1 (5–10% of the adult dose with proved metabolic responses). Endocrinological relationships between the donor’s load and the acceptor’s individual features are a new aspect of potential side effects of RBC transfusions. Further research is necessary to clarify the share of the described IGF administration on the development of ROP.

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