Hypoxia‐induced free iron release in the red cells of newborn infants*

Heparinized blood samples were obtained at birth from 164 newborn infants (101 full term; 63 preterm). Intra‐erythrocyte free iron concentration and hypoxanthine plasma levels were determined by high‐pressure liquid chromatography. Intra‐erythrocyte free iron concentration was higher in preterm than in full term babies (p < 0:0001) and adults (p < 0:0001). Statistically significant correlations were observed between intra‐erythrocyte free iron concentration and hypoxanthine levels (r = 0:66; p= 0:0001), pH (r = ‐ 0:76; p = 0:0001), base excess (r = ‐ 0:79; p= 0:0001), and gestational age (r = ‐ 0:44; p= 0:0001) in both infant populations. Multiple regression analysis between intra‐erythrocyte free iron concentration in cord blood, as an independent variable, and Apgar score at 1 min, pH, base excess, hypoxanthine values, FiO2 needed for resuscitation immediately after delivery, and gestational age, as dependent variables, identified hypoxanthine levels (p= 0:0003; partial F‐test = 15.4) as the best single predictor of intra‐erythrocyte free iron concentration. In conclusion, hypoxia induces intra‐erythrocyte free iron release, and therefore enhances the risk of oxidative injury due to hydroxyl radical generation.