LH (Luteinizing hormone): what does it say about you?

What is LH (luteinizing hormone)?

Luteinizing hormone, abbreviated as LH, is a hormone produced by the pituitary gland. This small gland is located at the base of the brain and acts as a kind of conductor of the endocrine system. LH transmits signals to the reproductive organs and has its own specific task in men and women.

In women, LH triggers ovulation: halfway through the menstrual cycle, the LH concentration in the blood peaks, after which the egg is released from the ovary. Subsequently, LH stimulates the production of progesterone and estrogen, hormones necessary for a potential pregnancy. In men, LH stimulates the Leydig cells in the testicles to produce testosterone, which is essential for sperm formation and sexual function.

LH works closely with FSH (follicle-stimulating hormone). Together, these two hormones regulate fertility and the hormonal cycle. Both are controlled by GnRH, a signaling substance released by the hypothalamus.

Why is LH measured?

An LH blood test provides insight into the functioning of the pituitary gland, the ovaries, or the testicles. Doctors use the results to determine the cause of hormonal complaints or to guide treatment.

Common reasons for having LH measured include:

• Investigation into fertility problems in men or women
• Irregular or missed periods
• Suspected PCOS (polycystic ovary syndrome)
• Assessment of pubertal development in adolescents
• Guidance of hormonal treatments, such as fertility therapy
• Suspected hypogonadism or a pituitary disorder

LH is measured via a simple blood draw. For women, the timing of the sample is important: the LH level varies depending on the phase of the menstrual cycle. Your doctor or laboratory will tell you when the measurement is most informative.

What can an abnormal LH level mean?

LH level that is too high

An elevated LH level in women can indicate a disruption of ovulation, such as in PCOS. In this condition, the ratio between LH and FSH is often disrupted, which makes egg maturation difficult. A high LH level can also be a sign that menopause is starting or has already set in: because the ovaries produce less estrogen, the inhibitory effect on the pituitary gland decreases and LH rises.

In men, an elevated LH level can indicate primary hypogonadism, a condition in which the testicles produce insufficient testosterone. The pituitary gland responds to this by releasing more LH, in an attempt to make the testicles work harder. In rare cases, a pituitary tumor can cause an overproduction of LH.

LH level too low

A low LH level usually indicates a problem higher up in the hormonal chain. When the hypothalamus produces too little GnRH, the pituitary gland does not receive a sufficient signal to produce LH. This can lead to fertility problems in both men and women.

A pituitary disorder, such as a tumor or damage to the gland, can also reduce LH production. Additionally, low LH levels can occur with severe underweight or anorexia nervosa: a chronic energy deficit profoundly disrupts the hormonal balance. Finally, persistent stress and psychological strain can affect hormone regulation from the brain, causing LH to drop.

When is it useful to have LH measured?

Have you been having trouble getting pregnant for a long time, are your periods irregular, or have they stopped altogether? In that case, an LH measurement is a logical step. LH can also provide relevant information if you have symptoms that could be consistent with menopause, or if your doctor wants to rule out a hormonal cause for fatigue or loss of libido.

LH is almost never assessed as a standalone value. The result is most informative in combination with FSH, estradiol, testosterone, and possibly prolactin. This creates a complete picture of how the hormonal axis between the brain and the reproductive organs functions.

Always discuss the result with a doctor. Values ​​outside the reference range do not automatically mean that something serious is wrong. Context matters: age, phase of the cycle, symptoms, and other blood values ​​together determine what a result truly means.