Luteinising hormone (LH)
May 11, 2021
What is LH?
Luteinising hormone is produced by the small gland at the base of the brain, the pituitary gland. It is important for fertility in both women and men.
In women, the levels of LH change depending on the time in the menstrual cycle. LH, together with follicle stimulating hormone (FSH), oestradiol and progesterone regulates a woman’s menstrual cycle. In the middle of the cycle, a sudden surge in LH and FSH leads to the release of eggs from follicles in the ovary. This process is called ovulation. When a woman reaches menopause, the surge of LH prior to ovulation disappears and the basal LH level increases.
In men, LH levels are relatively constant after puberty and stimulates the production of testosterone, the classic male sex hormone.
Why is this analysis important?
The LH test is an important complement to FSH and oestradiol in assessing menopausal status in women. Basal FSH and LH levels increase in women after menopause. However, due to variations in FSH and LH level during the menstrual cycle, one single measurement is often not enough to determine the menopausal status. Repeat testing is needed.
Normally, the ratio between LH and FSH is about 1:1 in menstruating women but in women with polycystic ovaries, the ratio is usually increased. Polycystic ovary syndrome (PCOS) is associated with fertility problems, obesity, acne and metabolic disorders such as type II diabetes.
Ovulation usually happens within 48 hours of a LH surge and therefore a LH test is also called a “ovulation test”. This is what ovulation home tests sold in pharmacies usually measure in the urine.
In both men and women, a LH test can be ordered together with a number of other hormone tests such as FSH, thyroid stimulating hormone (TSH), prolactin and growth hormone (GH) to investigate the function of the pituitary gland, in particular the anterior (front) part of it which secretes these hormones. When the pituitary gland is not functioning correctly, this can lead to vague symptoms such as fatigue, weakness.
In short, it is useful to analyse LH levels in the blood to:
Predict the time of ovulation in women;
Assess menopausal status in women;
Investigate irregular periods and fertility problems in women;
Identify the cause of low testosterone in men;
Investigate suspected pituitary disorders in both men and women.
The reference range for LH levels in the blood can be different depending on the laboratory and technique used. Doctors usually also take into account a number of factors when evaluating LH values.
High LH levels in the blood may be associated with:
Perimenopause or menopause
Test taken in mid-cycle phase of the menstrual cycle
Polycystic ovary syndrome (PCOS)
Low testosterone levels in men
Low LH levels in the blood may be associated with:
High levels of stress
Use of hormonal contraceptives
Low testosterone levels in men
LH levels fluctuate during the menstrual cycle. It is recommended for menstruating women to always take the test on day 3 in their menstrual cycle. For women who do not have menstrual cycles, and men, the test can be taken at any time.
Many hormonal contraceptives contain synthetic oestrogen which can interfere with the analysis of LH. It is therefore not recommended to take the test if you are taking hormonal contraceptives.
Corrine K Welt, MD. Evaluation of the menstrual cycle and timing of ovulation. UpToDate.