Copper is one of the essential trace elements in humans, and its deficiency causes various diseases. Zinc acetate dihydrate is administered to treat hypozincemia in preterm infants; however, zinc inhibits the gastrointestinal absorption of copper, which may cause copper deficiency. To safely treat hypozincemia in preterm infants, we retrospectively analyzed the factors reducing serum copper concentrations when zinc is administered to preterm infants with hypozincemia. Seventy preterm infants were included in the present study. Serum zinc and copper concentrations, doses, and other clinical characteristics were retrieved from electronic medical records. The administration of zinc acetate dihydrate decreased serum copper concentrations in 21 out of 70 patients. In comparisons between the two groups with and without a decrease in serum copper concentrations, significant differences were observed in postmenstrual age (34.9 and 35.9 weeks, respectively) and serum zinc concentrations (62.0 and 58.0 μg/dL, respectively) at the start of the zinc acetate dihydrate treatment. A logistic regression analysis identified postmenstrual age as a significant factor decreasing serum copper concentrations. In the ROC curve, the cut-off value for postmenstrual age for a decrease in serum copper concentrations was 34.143 weeks. The present results suggest that when zinc acetate dihydrate is administered to preterm infants with a low postmenstrual age who are at higher risk of decreased serum copper concentrations, particularly to those with a postmenstrual age <34 weeks, it is important to consider copper deficiency and periodically measure serum copper concentrations.
Keywords: copper; postmenstrual age; preterm infant; serum concentration; zinc.