The GnRH test (synonyms: Gonadotropin-releasing hormone test; gonadotropin-releasing hormone test; LH-RH test; LHRH test) is used to examine pituitary capacity. GnRH (gonadotropin-releasing hormone) is a hormone produced in the hypothalamus. It regulates the release of luteinizing hormone (LH) and follicle-stimulating hormone (FSH), which in turn control the sex-specific sex hormones. GnRH is released in a cyclic pulsatile manner.
The procedure
In the GnRH test, blood samples are taken before and several times after i. v. (intravenous) application of 100 µg GnRh (adults), or 60 µg/m2 (children): first blood sampling immediately before the start of the test (determination of basal LH and FSH levels), then after application of GnRH. Subsequently, after (25), 30, and (45) min, repeat blood draws and determination of LH and FSH individual levels.
Indications
- Differentiation of hypothalamic and pituitary (hypophysis) disorders.
- DD (differential diagnosis) of hypogonadism (gonadal hypofunction) (hypothalamic/pituitary cause).
- DD of pituitary tumors (endocrine active or inactive).
- DD of pubertas tarda (delayed onset of puberty; by definition, pubertas tarda occurs when boys do not show signs of pubertal development by age 14, and girls do not show signs of pubertal development by age 13)
- DD of pubertas praecox (premature onset of puberty; premature appearance of secondary sexual characteristics: in girls at the age of less than 8 years and in boys at the age of less than 9 years).
- Determination of functional reserve of gonadotropin secretion (due tolow gonadotropins) norm.
Norm values
| Gender | Parameter | Cycle | Normal value in U/I |
| Women | LH, 25 min after GnRH administration. | Follicular phase | <20 2-4-fold increase |
| Ovulation phase | <40 4-10 fold increase | ||
| Luteal phase | <30 3-8 fold increase | ||
| FSH, 45 min after GnRH administration. | ~ 10 | ||
| Men | LH, 25 min after GnRH administration. | 2-4-fold increase | |
| FSH, 45 min after GnRH administration. | 1.5-8 fold increase |
If an increase of at least threefold occurs, gonadotropic insufficiency (hormonal gonadal weakness) is excluded. Normal values boys
| Puberty stage | LH in IU/l 0 min | LH in IU/l 30 min | FSH in IU/l 0 min | FSH in IU/l 30 min |
| 1 (2-9 years) | < 0,3-2,5 | 1,3-3,8 | < 0,5-2,2 | 2,6-6,3 |
| 1 (> 9 years) | < 0,3-1,7 | 2,2-21,2 | < 0,5-2,5 | 3,5-6,9 |
| 2 | 0,3-1,7 | 3,3-18,9 | < 0,5-4,3 | 3,1-5,9 |
| 3 | 0,4-5,7 | 6,3-18,4 | 2,7-4,4 | 4,3-7,8 |
| 4 | 1,2-3,4 | 12,2-29,4 | 3,0-5,2 | 4,9-9,6 |
| 5 | 0,3-4,8 | 12,2-19,9 | 0,3-8,5 | 4,5-10,4 |
Normal values girls
| Puberty stage | LH in IU/l 0 min | LH in IU/l 30 min | FSH in IU/l 0 min | FSH in IU/l 30 min |
| 1 (2-9 years) | < 0,3-0,5 | 1,6-5,3 | < 0,5-3,2 | 6,8-16,2 |
| 1 (> 9 years) | < 0,3-2,0 | 1,6-11,3 | < 1,3-6,6 | 7,4-15,5 |
| 2 | < 0,3-1,2 | 3,3-17,4 | < 1,6-7,3 | 5,6-16,3 |
| 3 | 0,7-4,7 | 4,4-23,1 | 3,9-7,0 | 8,1-14,8 |
| 4 | 1,1-3,7 | 4,4-33,2 | 3,1-8,1 | 7,3-15,8 |
| 5 | 1,1-7,4 | 10,4-34,4 | 3,3-10,3 | 7,0-18,0 |
Stages of puberty (according to Tanner and Whitehouse).
- Prepubertal
- ♂ Testes (testicles) enlarged; ♀ Glandular body ≤ areola (areola) palpable.
- ♂ Testes and penis larger; ♀ Glandular body > areola.
- ♂ Penis larger, glans (glans) contour discernible; ♀ contour of areola detached.
- ♂ Adult; ♀ Adult.
Interpretation
Decreased increase
- Hypopituitarism (underactivity of the pituitary gland).
- Hypothalamic dysfunction (long-standing).
- Constitutional pubertas tarda
- Ingestion of hormones:
- Androgens
- Anabolic steroids (sex steroids)
- Estrogens
Increased increase or increased stimulability.
- Primary gonadal insufficiency (functional failure of ovary/ovary or testes/testis).
- Menopause (climacteric)
- Polycystic ovary syndrome (PCO syndrome; excessive stimulability of LH compared to FSH).
