Gonadotropin-releasing hormone stimulation test

The test checks the responsiveness or functional capacity of gonadotropin release to external LHRH administration. The test is only useful at low gonadotropin levels and without the intake of sex hormones.

Differential diagnosis of hypothalamic and pituitary hypogonadism. Distinction of constitutional developmental delay and hypogonadotropic hypogonadism

Blood collection (0 min - in the morning between 8.00 and 10.00 o'clock): Determination of the basal LH and FSH values

Application of 100 μg GnRH i.v. (children: 25 μg or 60 μg per^m2 body surface, 25 to a maximum of 100 μg GnRH)

Blood sampling (after 30 and 60 min; alternatively: every 30 min for 2 h, supplemented by estrogen/testosterone after 24 h): determination of stimulated LH and FSH levels

Reference ranges (the evaluation of the test results depends on age, sex, cycle phases and puberty stages). Compared to LH, FSH increases only with a delay and usually much less. The lower stimulability is without pathological significance.

Reference range for women (in IU/l) LH (25 min.p.i.)

• Follicular phase: <20 (2-4 times initial value)
• Ovulation phase: <40 (4-10 times initial value)
• Luteal phase: <30 (3-8 times output value)
• FSH (40 min.p.i.) Reference values (in IU/l): 10

Reference range for men (in IU/l) LH (25 min.p.i.)

• LH: 2-4 times output value
• FSH: 1.5-3 times the output value

Evaluations:

• Regular to high stimulability at low initial values: Indication of intact functional reserve in hypothalamic disturbance, an increase in LH > 3-fold in men and > 4-fold in women rule out a pituitary disturbance / gonadotropic insufficiency.
• Increased stimulability: evidence of polycystic ovaries (PCOS), postmenopause/climacteric, primary gonadal insufficiency.
• Lack of or low stimulability: pituitary insufficiency, prolonged hypothalamic disorder, pubertas tarda, intake of estrogens, androgens, anabolic steroids.
• Lack of stimulability: repeat test after one week of pulsatile GnRH administration with a pump (e.g. 5 μg GNRH 2 hourly; hypothalamic disorder: LH/FSH increase, hypophyseal disorder: LH/FSH increase absent)

Contraindication: therapy with GnRH analogues; pregnancy,

Discontinue sex hormones at least 3 weeks before the start of the test (e.g. oral contraceptives; testosterone depot preparations 6 weeks)

The test should only be carried out if the FSH and LH basal values are low; if the basal LH/FSH values are high, primary testicular (e.g. Klinefelter's syndrome) or primary ovarian hypogonadism must be considered.

In women, the optimal time for testing is in the luteal phase of the cycle (3rd-5th day of the cycle).

Measurement parameters: LH and FSH, in addition to the basal estrogen and testosterone levels.

1. Böhm C et al (2017) in: Neumeister B et al. clinical guide to laboratory diagnostics. Urban&Fischer Publisher Munich S. 345-347