What is LH?

Luteinising hormone (LH) is an important reproductive hormone for both men and women. In women, LH triggers ovulation and regulates the menstrual cycle, while in men, it stimulates testosterone production. 

An LH blood test can help investigate fertility issues, irregular periods, and testicular function. Normal levels vary by age, sex, and menstrual cycle phase. Abnormal levels can sometimes point to conditions such as PCOS, hypothyroidism, or pituitary disorders. In this article, we explore what your results could mean and what to do if your results are abnormal. 

We cover:

• What is LH?
• What does LH do?
• Reasons for testing
• Normal levels
• Low LH
• High LH
• LH and ovulation
• Checking LH levels
   

What is LH?

Luteinising hormone, or LH, is made by the pituitary gland in the brain. The pituitary gland is a pea-sized gland at the base of the brain. Alongside follicle-stimulating hormone (FSH), LH plays an important role in the reproductive system in both men and women.

How are LH levels controlled?

LH levels are regulated by a negative feedback loop involving the brain and the ovaries or testicles. Here’s how it works: 

1. The hypothalamus, an area of the brain, releases a hormone called gonadotropin-releasing hormone (GnRH). 
2. GnRH acts on the pituitary gland, another part of the brain, to stimulate LH release.
3. LH travels either to the testicles to trigger testosterone release, or to the ovaries to trigger ovulation and the release of oestrogen and progesterone.
4. Higher levels of testosterone, oestrogen, and progesterone inhibit GnRH and LH release to prevent hormone levels from becoming too high. 

This system ensures that hormone levels stay within the optimal range. 
 

What does LH do?

Luteinising hormone is a gonadotrophic hormone, meaning it acts on the gonads (testicles and ovaries), triggering certain processes. 

In women, LH: 

• Triggers ovulation – During ovulation, LH levels surge causing the ovarian follicle to release an egg around the middle of the cycle. The LH surge is sometimes used as an indicator of fertility and to help identify the most fertile days in a woman’s cycle. 
• Helps form the corpus luteum – After ovulation, LH stimulates the remains of the follicle to transform into the corpus luteum (luteinisation), which is how luteinising hormone gets its name.
• Regulates the menstrual cycle – At the beginning of the cycle, LH works with FSH to promote the growth and maturation of the ovarian follicles. After ovulation, LH stimulates the corpus luteum to produce progesterone, which is important to support the early stages of pregnancy if fertilisation occurs.

In men, LH: 

• Stimulates the testicles to produce testosterone – LH binds to Leydig cells in the testicles, stimulating them to produce and release testosterone.

Why do I need an LH test?

An LH blood test can be useful to investigate problems with fertility, periods, or testicular function.

Common reasons for checking LH levels: 

In women

• Investigating abnormal periods
• Checking whether ovulation has occurred
• Monitoring fertility treatments
• Helping to diagnose menopause if it’s occurring earlier than expected or if symptoms are atypical

In men

• Investigating low testosterone levels or associated symptoms such as low libido
• Checking testicular function

In both women and men

• Investigating causes of infertility
• Checking the pituitary gland is working normally
   

What’s a normal LH level?

A normal LH level will depend on your age, sex, and when you took the test. 

Normal ranges vary from lab to lab. The reference ranges below serve as a guide only.
 

LH surges around 24–36 hours before ovulation. In the second half of the cycle (luteal phase), LH levels return to their baseline. During pregnancy, LH levels remain very low, blocked by continued progesterone production.
 

What might a low LH level mean?

A low level of LH may be due to several potential issues, often related to lifestyle factors or problems with the pituitary gland or hypothalamus.

Causes of low LH include:

• Stress, extreme exercise, malnutrition, or being very underweight – These are some of the most common causes of a low or low-normal LH result.
• Hypothyroidism – Some studies show that an underactive thyroid decreases levels of LH [1]. 
• Kallmann syndrome – This rare genetic disorder causes small testicles, low testosterone, a lack of sense of smell, and low LH. 
• Sheehan syndrome – Also known as postpartum hypopituitarism, this rare syndrome can occur in women with very low blood pressure during childbirth.
• Pituitary disorders – Tumours affecting or compressing the pituitary can directly impact the production and release of LH.
   

Symptoms of low LH

The symptoms of low LH will depend on the underlying cause. 

Symptoms of low LH in women: 

• Irregular periods
• Hot flushes
• Infertility
• Low libido
• Delayed puberty
• Fatigue

Symptoms of low LH in men:

• Low libido
• Infertility
• Erectile dysfunction
• Delayed puberty
• Fatigue
   

How to increase LH levels

If low LH levels are due to lifestyle factors, it’s important to make sure you have a healthy, balanced diet, exercise regularly (but not too much), and manage stress as best as you can. 

For other medical causes of low LH, you may need hormone therapy that can help stimulate LH release to increase your overall levels. 

What might a high LH level mean?

A high LH level is often caused by a problem with the ovaries or testicles. If they can’t make enough of the sex hormones (i.e. oestrogen or testosterone), the pituitary gland attempts to compensate by releasing more FSH and LH. This is called primary ovarian failure or primary testicular failure. 

High LH can also be a direct problem with the hypothalamus or pituitary gland.

Causes of high LH in women:

• Taking your sample at the wrong time – Most hormone fertility tests are taken on day three of your cycle when LH levels are at their lowest. If you take your sample later, your result may appear high against the day three reference range. (To predict ovulation, however, LH tests are typically taken mid-cycle.)
• Polycystic ovary syndrome (PCOS) – PCOS is a common condition characterised by an imbalance of hormones and insulin resistance. It disrupts the normal hormone feedback mechanisms leading to a raised LH relative to FSH. 
• Primary ovarian insufficiency (POI) – When the ovaries stop functioning before age 40. 
• Menopause – LH levels naturally increase during and after menopause due to the decline in ovarian function.
• Turner syndrome – Turner syndrome is a genetic condition where one of the X chromosomes is completely or partially missing. It leads to underdeveloped ovaries, low oestrogen, and raised LH.

Causes of high LH in men:

• Injury to the testicles – This could be a direct injury to the testicles or a low-level injury, like prolonged cycling. 
• Undescended testicles at birth
• Testicular cancer – Rates of testicular cancer peak between ages 30 and 34 but can occur at almost any age.
• Testicular torsion – This is a surgical emergency where one of the testicles becomes twisted, affecting its blood supply.
• Mumps – Mumps is a viral infection that used to be common in children before the MMR vaccine. One of the complications of mumps is inflammation of the testicles (orchitis).

Causes of high LH in both sexes: 

• Hyperthyroidism – Small-scale studies have shown that people with Graves’ disease (an overactive thyroid condition) have increased LH secretion [2]. 
• Chemotherapy or radiotherapy – Cancer treatmentscan affect ovarian and testicular function. The pituitary gland attempts to compensate by producing more LH. 
• Pituitary gland tumours – Just as pituitary tumours can cause low LH levels, sometimes a tumour can cause the pituitary to make too much LH. 
   

Symptoms of high LH

The symptoms of raised LH levels are usually due to the underlying condition. 

Symptoms of high LH: 

• Infertility
• Irregular periods in women
• Erectile dysfunction in men
• Mood swings
• Fatigue
• Low libido
   

How to lower LH levels

Reducing LH levels will depend on why your LH levels are raised. For example, metformin may be helpful for women with PCOS. Hormone replacement therapy (HRT) can be an effective treatment for premature ovarian insufficiency (POI). Thyroid medications or surgery can help correct an overactive thyroid. 

Maintaining a healthy lifestyle is also likely to have a positive effect on your hormones. Find out more about how you can balance your hormones naturally. 
 

How long after an LH surge do you ovulate?

Ovulation usually happens 24 to 36 hours after an LH surge. Therefore, LH levels are an excellent way of determining when your most fertile window is likely to be. 

Peak fertility is the day of ovulation and the day before, but fertility remains high for a few days before this because sperm can survive for up to five days in the reproductive tract.

How can I check my LH levels?

You can check your LH levels at home with a simple Female Hormone Blood Test or Male Hormone Blood Test. 

If you want to determine your fertile window, we recommend a urinary LH kit. This allows you to take multiple tests over different days to pinpoint ovulation.
 

What to do if your LH levels are abnormal

If your LH levels are abnormal, it’s best to speak to your doctor who may advise additional tests to identify the underlying cause. If your levels are only slightly outside the normal range, you may wish to re-check your levels several weeks later, after making healthy changes to your lifestyle. Our doctors will always advise you on what to do next if your result is abnormal. 
 

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References

1. Acharya N, Acharya S, Shukla S, Inamdar SA, Khatri M, Mahajan SN. Gonadotropin Levels in Hypothyroid Women of Reproductive Age Group. J ObstetGynaecol India. 2011;61: 550–553. doi:10.1007/s13224-011-0079-7
2. Zähringer S, Tomova A, Werder K von, Brabant G, Kumanov P, Schopohl J. The influence of hyperthyroidism on the hypothalamic-pituitary-gonadal axis. Experimental and Clinical Endocrinology & Diabetes. 2000;108: 282–289. doi:10.1055/s-2000-7756