Effect of gender and age on fasting serum growth hormone levels in normal subjects

Fasting growth hormone (GH) level is an important reference level in dynamic tests of GH secretion. Other studies have demonstrated sex and age variation in the rate of GH secretion. We analysed fasting serum samples from 377 normal subjects (193 males and 184 females, age range 6 to 81 years old), using our in-house enzyme immunoassay. We found sex differences in fasting GH levels to be only significant in the prepubertal children (Tanner stage I), being higher in girls than in age-matched boys (p < 0.05). Both sexes showed age-dependent changes in fasting GH levels (p < 0.001); highest levels were achieved at puberty and subsequently declined with advancing age. Hence, the physiological sex difference and age-dependency in GH secretion can also be demonstrated in single fasting samples.