Normal total plasma calcium in the newborn

The first week of human life is characterized by rapidly changing plasma calcium levels, as well as low concentrations in comparison with adults. Whereas the infant's cord blood has a higher concentration than the mother's blood, the level drops precipitously in the first 24 hr (first drop) after birth and reaches a minimum level (second drop) at about 48 hr. A third drop may follow between the fourth and seventh days, but is different from the other two in that it is generally preventable with proper milk feeding. The level is markedly influenced by starvation, diet, and age. During the first week, the full-term newborn may show calcium levels in the range of 1.75 to 3.00 mmol/1, whereas the premature newborn shows values of 1.50 to 2.50 mmol/1. The low birth weight infant displays intermediate values. The literature on diseases involving calcium in the newborn, particularly neonatal tetany, is especially helpful in establishing a concept of normal levels, providing clinically supported upper and lower values. Calcium studies on the new born have been notably advanced by use of sound ultramicrochemical analytical methods.