Total and Unbound Testosterone Levels in the Newborn and in Normal and Hypogonadal Children: Use of a Sensitive Radioimmunoassay for Testosterone

Abstract

A sensitive and reliable radioimmunoassay combined with celite column chromatography for specific determination of plasma testosterone (T) is described. The percentage binding was measured by equilibrium dialysis. In 28 normal newborns, total T concentration is significantly higher in male (68.1 ± 59.5) than in female newborn infants (12.0 ± 6.2) while binding of T increases rapidly after birth. Although there is no sex difference in TeBg capacity, levels of unbound T in the first two weeks of life are still significantly higher in male than in female infants. There was no sex difference in 62 normal prepubertal children studied, the total T concentration being 6.62 ± 2.46 and 6.58 ± 2.48 ng/100 ml in boys and girls, respectively; the binding of T and unbound T levels were identical in both. In 17 patients with Turner syndrome, total T concentration (13.6 ± 3.1 ng/100 ml) was significantly higher than in prepubertal children and increased (21.5 ± 2 ng/100 ml) under moderate estrogen therapy while the percentage of T bound to protein did not change (96.65% ± 0.29 and 96.81% ± 1.4 respectively). However unbound T levels remained 1/4 to 1/2 that of normal adult females. In 13 patients with primary hypogonadism, total T concentration was similar to that of Turner patients (13.12 ± 5.4 ng/100 ml) so as were the percentage of T bound to proteins and unbound T levels. The physiological implications of free and bound testosterone concentrations in newborns, prepuberal and hypogonadal children are discussed.