Luteinizing hormone (LH)

Luteinizing Hormone (LH) is an important reproductive hormone in both women and men. It’s produced by the pituitary gland, and its levels in the blood are maintained by the HPG axis; an endocrine circuit responsible for regulating reproductive function. LH allows ovulation to happen in the female ovaries, and facilitates the production of testosterone in the male testes.

For women, tracking LH levels can be very useful for the purpose of family planning. Certain symptoms can also point towards abnormal LH levels, in which case one may wish to consider getting an LH test.

Read on to learn about LH, what it does, how and why it is tested, and more.

Luteinizing Hormone (LH) is a reproductive hormone produced by the pituitary gland in the brain. It is a ‘gonadotropin’ hormone, which means that it exerts its effects in the gonads – the testes in men, and the ovaries in women. Follicle Stimulating Hormone (FSH) is another gonadotropin produced by the pituitary and works together with LH to facilitate and regulate reproductive function in both men and women. 1

LH levels in the body are regulated by an important endocrine axis called the Hypothalamic-Pituitary-Gonadal (HPG) axis. The hypothalamus, pituitary gland, and gonads are the three key elements in this system. Signaling between the three elements of the HPG axis works to maintain the correct LH (and FSH) levels in the blood, and can be summarized as follows: 1 2

1. The hypothalamus, which sits in the brain, releases pulses of Gonadotropin-Releasing Hormone (GnRH);
2. GnRH stimulates the production and release of LH from the pituitary gland;
3. LH travels to the gonads and acts on cells in the female ovaries and male testes;
4. This results in, among its other effects, the production of testosterone and estradiol;
5. Testosterone and estradiol levels in the blood are ‘monitored’ by the hypothalamus, and inform it if more or less LH is required. This is called the “negative feedback loop”, which is a type of self-regulating system.

LH plays different roles in men and women, although it is vital to healthy reproductive function in both sexes.

In women, LH has many functions throughout the menstrual cycle. In the first half of the cycle, LH acts on the maturing follicle, resulting in the production of estradiol. Towards the middle of the cycle, estradiol levels peak, which causes the LH surge. When this happens, LH levels rapidly rise to very high levels. This is a crucial element of the female reproductive cycle, as it directly results in ovulation – the release of an egg from the now mature follicle. After the surge, LH levels promptly drop again. During the second half of the menstrual cycle, LH acts on the remnant of the burst follicle, called the corpus luteum, stimulating it to produce progesterone. 2 3

In men, LH acts on a group of cells in the testes called the Leydig cells. These cells are responsible for the production of testosterone, the main male reproductive hormone. Therefore, LH is responsible for testosterone activity in men, which influences sperm production and the development of secondary sexual characteristics such as a deep voice or facial hair. 2 4

If you are a woman, the amount of LH circulating in your blood will vary based on the stage of your menstrual cycle. If you are a man, your LH levels should remain consistent. The National Health Service (NHS) in the United Kingdom cites the following as normal LH level ranges for adults: 5

Women

• Days 1-14 (Follicular phase): 1-12 IU/L
• Day ~14 (Ovulation): 16-104 IU/L
• Days 14-28 (Luteal phase): 1-12 IU/L

Men

• 1-8 IU/L

Importantly, normal FSH and LH levels vary by age. The pituitary gland also produces low levels of LH in prepubescent children, typically between 1-5 IU/L. LH levels also rise naturally after a woman goes through menopause. 5

Tracking your LH levels can be very useful if you are trying to conceive. If you know when your LH surge happens, you can roughly estimate when your fertile window started, and when it is going to end. The fertile window describes the few-day period during which you are most likely to become pregnant if you have sex. It begins up to 5 days before ovulation and lasts for around a week. Two types of LH hormone tests exist: blood tests and urine tests. LH urine tests are commonly known as ovulation tests, and can often be bought over the counter. Both of these tests are highly accurate. 6

Having a good understanding of how all of your reproductive hormones work together can be very insightful, especially when it comes to matters of fertility. The interplay of LH with FSH, estradiol, and progesterone in women is complex. Tools such as an LH levels chart or a menstrual hormone chart can help visualize their levels with more clarity. You can explore a good example of this type of chart in the introduction section of this paper. 7

LH directly influences reproductive function in both men and women. Because of this, its levels are often checked if a couple is experiencing trouble with conceiving. LH is also closely monitored if a woman is being treated with assisted reproductive technologies, such as IVF. When trying to conceive, a woman may wish to use home ovulation test kits to be more informed as to her fertile window. These kits detect LH from urine. 1 6

In females, irregular periods, early symptoms of menopause, and early or delayed puberty can all be suggestive of a disturbance in LH levels. In males, symptoms of low testosterone can indicate that circulating LH is low. If you experience any of these symptoms, you may wish to consider an LH test. 4 5

An LH blood test is a simple procedure in which a small sample of blood is taken from a vein in the arm. If you are referred for such a test, your doctor will direct you as to when you should have the sample taken.

FSH and LH are both hormones produced in the front part of the pituitary gland, and are both regulated by the HPG axis. They work together to influence cells in the gonads, which is why their balance in the blood is so important for maintaining reproductive function.

In women, FSH and LH act together on different cells in the ovaries to facilitate the maturation of an egg and its ovulation every month. Both hormones are also important after ovulation, although the LH-dependent maintenance of the corpus luteum is most important at this stage. 3 The proportion of circulating LH to FSH, also called the LH:FSH ratio, is a measurement that is used to help with diagnosing polycystic ovarian syndrome (PCOS) in women. If you have PCOS, the LH:FSH ratio will likely be higher than 1. 5

In men, FSH and LH act on different cells in the testes to regulate reproductive function. The Sertoli cells, which are responsible for the maturation of immature sperm cells, are acted on by FSH. Meanwhile, LH facilitates the production of testosterone by stimulating the Leydig cells. 4

Q: What is an LH surge?
A: An LH surge happens around day 14 of a woman’s menstrual cycle when LH levels rise rapidly before dropping back to baseline again. It directly results in ovulation.

Q: What LH level indicates ovulation?
A: A blood LH level of 16-104 IU/L, measured around day 14 of a woman’s menstrual cycle, indicates ovulation.

Q: Does LH surge always mean ovulation?
A: An LH surge results in ovulation the vast majority of the time. However, Luteinized Unruptured Follicle Syndrome is a condition in which the follicle does not rupture after the LH surge, and therefore ovulation does not happen. 8

Q: How long after LH surge do you ovulate?
A: Ovulation normally occurs 35-44 hours after the LH surge starts. 6

Q: How long does LH stay elevated after ovulation?
A: The LH surge normally happens just over a day before ovulation itself. Because of this, LH levels return to their low baseline levels before ovulation actually happens, and are therefore low after ovulation.

Q: Does LH surge stay high if pregnant?
A: LH levels always return to baseline after the surge, even if fertilization and pregnancy occur after the egg is ovulated in that cycle. In fact, rather than being higher, LH levels during pregnancy are significantly lower than normal.

Q: Is LH involved if there is spotting during ovulation?
A: Ovulation bleeding, or ‘spotting’, around the middle of your cycle does not point towards any health issues in most women who experience it. One study has suggested that women with naturally higher levels of progesterone, and women over the age of 30 are more prone to spotting. 9

Q: What is an LH surge chart?
A: Some women choose to keep a log of when their LH surges happen each month using an LH surge chart. Doing so can give you an insight into when you are most fertile, which helps with family planning.