Luteinizing hormone, also referred to as LH, is a hormone produced by the pituitary gland. In women, is responsible for the maturation of follicles, ovulation and production of progesterone, and therefore plays a fundamental role in a woman's reproductive capacity. In men, LH is also directly related to fertility, and acts directly on the testicles to trigger sperm production.
In the menstrual cycle, LH levels are higher during ovulation, however it is present in the blood throughout the cycle and the woman's lifetime.
In addition to playing an important role in fertility, LH levels can be tested to help diagnose pituitary tumors and to identify any abnormalities in the ovaries, like the presence of cysts.
Luteinizing hormone tests can be ordered for the following reasons:
- Diagnose infertility
- Assess sperm production
- Assess for the likelihood of menopause
- Determine what is causing the absence of a period
- Evaluate egg production in women
- Help with the diagnosis of a pituitary tumor
In men, LH production is regulated by the pituitary gland and acts directly on the testicles. It helps to regulate sperm production as well as the production of other hormones, mainly testosterone. In women, LH production in the pituitary gland stimulates the production of progesterone and estrogen, which are essential for pregnancy.
To assess fertility in men and women, the doctor may also request an FSH blood test. This hormone is also present in different levels during the menstrual cycle and can also influences sperm production.
The normal reference levels for luteinizing hormone vary according to age, gender and phase of the menstrual cycle.
- Children: less than 0.15 U/L
- Men: between 0.6 - 12.1 U/L
- Women in the follicular phase: between 1.8 and 11.8 U/L
- Women at ovulatory peak: between 7.6 and 89.1 U/L
- Women in the luteal phase: between 0.6 and 14.0 U/L
- Menopause: between 5.2 and 62.9 U/L
Test results should be evaluated by the ordering doctor, who will consider other test results and the physical assessment to determine a diagnosis.
Low LH levels
Low LH levels may be a sign of:
- Pituitary gland abnormalities that cause a reduced production of LH and FSH
- Deficiency in the production of gonadotropin (GnRH), which is a hormone produced and released by the hypothalamus. Its function is to stimulate the pituitary gland to produce LH and FSH;
- Kallmann syndrome, which is a genetic and hereditary disease characterized by the absence of GnRH production, which leads to hypogonadism;
- Hyperprolactinemia, which is an increase in the production of prolactin hormone.
A decrease in LH can lead to reduced sperm production in men and in the absence of menstruation in women, a situation known as amenorrhea. It is important to consult a doctor so that the best treatment can be indicated, which is normally done with the use of hormonal supplementation.
High LH levels
High LH levels may be a sign of:
- Tumor in the pituitary gland, with an increase in the secretion of GnRH and, consequently, LH
- Early puberty
- Testicular insufficiency
- Early menopause
- Polycystic ovarian syndrome
Furthermore, the LH hormone may be increased during pregnancy, as beta-hCG can imitate LH, causing it to appear elevated on tests.