Luteinizing Hormone (LH): Function, normal levels, and when testing is useful

Hormonal balance influences numerous processes in the body—from fertility and the menstrual cycle to testosterone production. A key role in this system is played by luteinizing hormone (LH). Among other functions, it regulates ovulation in women and testosterone production in men and provides important insights into the functioning of the hormonal regulatory system.

In this article, you will learn what luteinizing hormone is, which roles it plays in the body, which LH levels are considered normal, when testing is useful, and how abnormal values can be medically interpreted.

Table of Contents

• What is luteinizing hormone (LH)?

• What function does LH have in the body?

• Which LH levels are normal?

• When is an LH test useful?

• What do high or low LH levels mean?

• How should LH values be interpreted correctly?

• Summary

What is luteinizing hormone (LH)?

Luteinizing hormone, abbreviated as LH, is a hormone produced naturally by the body and belongs to the group known as gonadotropins. It is produced in the pituitary gland and transported via the bloodstream to the reproductive organs.

LH acts on the function of the gonads (ovaries in women and testes in men) and is therefore a central component of the hormonal regulation of fertility and sex hormone production (MedlinePlus, 2023, NIH, 2025).

What function does LH have in the body?

The effects of luteinizing hormone differ depending on sex but always serve the same overarching purpose: regulating the production of sex hormones.

In women

• Triggering ovulation through a short-term surge in LH

• Supporting the maturation of the egg cell

• Stimulating the formation of the corpus luteum, which is responsible for progesterone production

In men

• Stimulating Leydig cells in the testes to produce testosterone

• Indirectly supporting sperm production through regulation of hormonal balance

Source: Cleveland Clinic, 2025

How is LH secretion regulated in the body?

LH secretion does not occur in isolation but is part of a finely tuned hormonal control system known as the hypothalamic–pituitary–gonadal axis.

• The hypothalamus releases the hormone GnRH.

• This stimulates the pituitary gland to secrete LH and FSH (follicle-stimulating hormone).

• LH and FSH act together on the ovaries or testes and regulate the production of sex hormones.

Especially in cases of menstrual cycle disorders or infertility, the interaction between LH and FSH is crucial for medical assessment.

Which LH levels are normal?

The concentration of luteinizing hormone in the blood depends on age, sex, and—in women—on the phase of the menstrual cycle.

Note: Reference ranges may vary slightly between laboratories. LH values should always be interpreted in relation to the day of the cycle and in conjunction with other hormone levels (NHS, 2024, MedlinePlus, 2023).

Brief overview of the menstrual cycle phases

The menstrual cycle is divided into several phases. The follicular phase begins on the first day of menstruation and lasts on average about 10–14 days. During the ovulatory phase, ovulation occurs around the midpoint of the cycle and usually lasts only one to two days. In the subsequent luteal phase (approximately 12–14 days), the body prepares for a possible pregnancy before the cycle begins again with the next menstrual period (Cleveland Clinic, 2022).

When is an LH test useful?

An LH test can provide valuable information about hormonal status and is commonly used in the following situations:

• Menstrual cycle disorders or absence of menstruation

• Infertility

• Suspected premature menopause

• Polycystic ovary syndrome (PCOS)

• Monitoring ovulation when trying to conceive

• Evaluation of reduced hormone production in men

How is an LH test performed?

In medical diagnostics, luteinizing hormone is typically measured using a blood test. In women, the timing of blood sampling is particularly important, as LH levels change significantly over the course of the menstrual cycle (MedlinePlus, 2023).

Urine tests are also used for cycle tracking. These so-called ovulation tests detect the short-term LH surge that occurs approximately 24 to 36 hours before ovulation. They help identify the fertile window but do not replace comprehensive hormonal diagnostics.

Testing in a medical practice or at home

In addition to testing in a medical practice, LH levels can also be measured at home using a finger-prick blood sample, for example with the Luteinizing Hormone Test by Homed-IQ. For a more comprehensive assessment, it may be useful not to measure LH in isolation but to analyze multiple hormones together—for example through the Fertility Test for Women or the Hormone Test for Women—to better evaluate overall hormonal status.

What do high or low LH levels mean?

Values outside the normal range can indicate various underlying causes but must always be evaluated in the overall clinical context.

Possible causes of elevated LH levels

• Polycystic ovary syndrome (PCOS)

• Premature menopause (primary ovarian insufficiency)

• Functional impairment of the testes in men

• Rare disorders affecting the pituitary gland

Possible causes of low LH levels

• Disorders of pituitary function

• Severe underweight or eating disorders

• Intense physical exertion or chronic stress

• Use of hormonal contraceptives (physiological suppression of LH secretion)

Source: Cleveland Clinic, 2025

How should LH values be interpreted correctly?

A single LH value allows only limited conclusions. For a well-founded assessment, the following factors should be taken into account:

• Cycle day in women

• The ratio of LH to FSH

• Accompanying symptoms

• Additional hormone levels such as estrogen, progesterone, or testosterone

A holistic hormonal assessment is particularly important in cases of infertility or menstrual cycle disorders.

When should medical advice be sought for abnormal LH levels?

If LH levels are significantly elevated or reduced, if symptoms persist, or if infertility is present, medical evaluation is recommended. Physicians can order additional tests and interpret the results within the full medical context. A hormone test can provide an initial orientation but does not replace individualized medical advice or diagnostic evaluation.

Summary

Luteinizing hormone (LH) plays a central role in ovulation, testosterone production, and fertility. Because LH levels vary depending on cycle phase and hormonal interactions, they must always be evaluated within the broader medical context. An LH test can provide initial insights but does not replace medical assessment.