Gonadotropin releasing hormone agonist (nafarelin) test to differentiate gonadotropin deficiency from constitutionally delayed puberty in teen-age boys--a clinical research center study.

The objective of this study was to determine whether the hormonal response to a GnRH agonist (nafarelin) challenge differentiates hypogonadotropinism from delayed puberty as well as the sleep test does. We studied boys ages 13.25-17.6 yr with prepubertal constitutional delay of puberty (CDP, n = 11), prepubertal gonadotropin deficiency (GnD, n = 10), pubertal CDP (PCDP, n = 11) and partial GnD (PGnD, n = 2). These disorders were defined on the basis of the following independent criteria: CDP = isolated delayed puberty with documentation of subsequent pubertal progression; GnD = panhypopituitarism or anosmia with absence of subsequent pubertal progression; PCDP = isolated delayed puberty in an early pubertal child; and PGnD = arrest of puberty in boys with partial hypopituitarism. CDP was compared with GnD and PCDP was compared with PGnD by analysis of variance and two-tailed t tests. Each patient had a nafarelin test with measurement of LH, FSH, and testosterone responses at intervals after nafarelin administration. Most patients had a sleep test with measurement of LH and testosterone levels at intervals overnight. CDP and GnD patients could not be distinguished by pubertal staging criteria. All but 1 patient with CDP had an LH response higher than that of GnD patients 4 h postnafarelin (P = 0.003). An incremental response to nafarelin of LH (delta LH at 4 h) below 4.8 IU/L was the best discriminant; it distinguished GnD from CDP in 95% of the cases and PGnD from PCDP completely. During the sleep test, all patients with CDP and 2 of 8 with GnD exhibited a significant increase in plasma LH. An incremental increase in LH during sleep (mean LH asleep minus mean LH awake) of less than 0.35 IU/L, near the limit of sensitivity of the method, differentiated GnD from CDP similarly to the nafarelin test. We conclude that the LH response to nafarelin distinguished gonadotropin deficiency from constitutional delay of puberty as well as the sleep test did and with certain advantages. The diagnostic reliability of the GnRH agonist test deserves to be determined prospectively in teen-agers with isolated GnD and partial hypopituitarism.