Luteinising Hormone (Blood)

Diagnostic Use

In males, a low plasma testosterone with low or “normal” LH and FSH values is suggestive of secondary hypogonadism (hypothalamic or pituitary disease), while a high LH and FSH suggests primary testicular dysfunction.

In females, elevated LH and FSH are seen after menopause or premature ovarian failure, and in primary ovarian dysgenesis (e.g. Turners syndrome). Amenorrhoea with low LH and FSH is seen in central delayed puberty, hypothalamic or pituitary disease.

Timing of ovulation: the midcycle peak of LH precedes ovulation by 24-36 hours.

The ratio of LH to FSH is usually increased (>2) in the polycystic ovary syndrome, but a ratio less than this does not exclude this diagnosis.

LH is released in a pulsatile manner and wide fluctuations may be found from hour to hour.

Reference Intervals

From 15/06/22, the plasma LH and FSH age- and gender-specific reference intervals together with related comments have been revised for young children and adolescents during puberty. This review has been endorsed by the Auckland Regional Quality Assurance Group (ARQAG) in May 2022 after consultation with local paediatric endocrinologists. There has not been any change to the corresponding reference intervals for post-pubertal adults.

Units: IU/L

Reference ranges

Paediatric (<16 years old):

0 – 1 year: 

The reference interval for LH is not well defined for this age.  A paediatric endocrine opinion is suggested.

1 – 16 years: 

In the setting of delayed puberty or suspected CPP (central precocious puberty): an early morning LH <0.3 IU/L suggests activation of the HPG (hypothalamic-pituitary-gonadal) axis is less likely but not excluded.  An LH >0.8 IU/L supports clinical findings of central activation of the HPG axis.
A repeat investigation may be useful to allow for pulsatile release of LH, if the sample was not collected within approximately 2 hours from waking or if the result is indeterminate.
Suggest discussion with a paediatric endocrinologist if in doubt.