1. To assess the level of LH/FSH pituitary reserve.

2. To investigate pubertal disorders:

   1. precocious puberty
   2. premature breast development in girls (thelarche)
   3. delayed puberty.

1. This test may be combined with Growth Hormone stimulation tests; increase the volumes of blood collected if combined with other tests.
2. Avoid HCG injections during the test as cross-reaction in LH analyses gives falsely elevated results.
3. Fasting is not required.
4. Timing of the test is not important unless it is combined with the insulin hypoglycaemia test.

Drug(s) Given

Gonadorelin (LHRH, GnRH) 100 micrograms.

How Given

Intravenously as a slow bolus.

Timing of Administration

After baseline bloods taken.

The LHRH test can be difficult to interpret and results should be interpreted alongside clinical findings.
These include:

• Full pubertal staging.
• Testicular volume in boys.
• Ovarian ultrasound in girls.

Puberty is a continuum and so is the response to the GnRH test.

Pre-pubertal response:

• LH peak less than 5U/L (or an LH increment less than 3-4U/L above basal).
• FSH peak greater than LH (or an FSH increment less than 2-3U/L above basal)

Peri-pubertal and pubertal response:

• Higher increments, especially if the LH response is dominant provides evidence of a pubertal pattern of gonadotrophin response.
• LH peak greater than 5U/L.
• LH peak greater than FSH peak.

Precocious puberty:

Gonadotrophin-independent precocious puberty:

• Spontaneous gonadotrophin secretion is suppressed by the autonomous sex steroid secretion
  Basal LH/FSH is low.
• Response to LHRH is flat.

Gonadotrophin-dependent precocious puberty:

• Basal LH/FSH levels are usually (but not always) elevated.
• Response to LHRH is exaggerated.

Precocious puberty (treated):

• Suppressed basal LH/FSH.
• Flat response to LHRH.

Indicates adequate treatment with LHRH analogues. However, repeat LHRH test on treatment is not usually necessary.

Premature thelarche and thelarche variant:

• LH response is usually in the prepubertal range.
• FSH response is predominant.

Pubertal Delay and Pubertal failure:

Children with suspected hypogonadotrophic hypogonadism (HH):

• Complete lack of response supports the diagnosis.

However, a measurable but low response (in the pre-pubertal range) may occur both in HH and in constitutional delay of puberty and has limited predictive value.

Note that the LHRH test does not differentiate between HH and pubertal delay.

Primary gonadal failure:

• Basal LH and FSH are elevated.
• LH and FSH response to GnRH is exaggerated.

1. K Ghai, JF Cara, and RL Rosenfield Gonadotropin releasing hormone agonist (nafarelin) test to differentiate gonadotropin deficiency from constitutionally delayed puberty in teenage boys: a clinical research center study. J. Clin. Endocrinol. Metab. 1995 80: 2980-2986.