What is lh in blood test

Last updated: April 1, 2026

Quick Answer: LH (Luteinizing Hormone) is a hormone produced by the pituitary gland that regulates reproductive function. Blood tests measure LH levels to assess fertility, hormone imbalances, and menstrual cycle health.

Key Facts

Overview

Luteinizing Hormone (LH) is a crucial reproductive hormone measured in blood tests to evaluate hormone balance and fertility status. The pituitary gland, located at the base of the brain, produces LH in response to signals from the hypothalamus.

Role in Reproduction

In women, LH plays a critical role in the menstrual cycle. A surge in LH levels triggers ovulation, the release of an egg from the ovary, typically occurring around day 14 of a 28-day cycle. LH also stimulates the corpus luteum to produce progesterone, essential for maintaining pregnancy. In men, LH stimulates the Leydig cells in the testes to produce testosterone, which is necessary for sperm production and sexual function.

Normal Ranges

LH levels vary significantly based on sex, age, and menstrual cycle phase. In women, normal follicular phase levels are typically 1.7-15 IU/L, while ovulation surge levels can reach 21-160 IU/L. In men, normal levels are approximately 1.7-8.6 IU/L. Postmenopausal women have elevated LH levels, typically 15-62 IU/L.

Why LH Tests Are Ordered

Healthcare providers order LH blood tests to diagnose fertility problems, irregular menstrual cycles, hormonal imbalances, and pituitary gland disorders. The test is commonly used in fertility evaluations and to monitor hormone replacement therapy.

Abnormal Results

Low LH levels may indicate pituitary dysfunction, hormonal disorders, or malnutrition. Elevated LH levels can suggest ovarian failure, PCOS (Polycystic Ovary Syndrome), menopause, or primary hypogonadism in men.

Related Questions

What is the normal range for LH levels?

Normal LH ranges vary by sex and cycle phase: women in follicular phase typically have 1.7-15 IU/L, ovulation surge 21-160 IU/L, and men have 1.7-8.6 IU/L. Postmenopausal women have significantly higher levels at 15-62 IU/L.

What is the difference between LH and FSH?

Both are pituitary hormones regulating reproduction. FSH stimulates follicle development and sperm production, while LH triggers ovulation and testosterone production. Both are tested together for fertility assessment.

What is the normal LH level for women?

Normal LH levels vary by menstrual cycle phase: 5-20 IU/L during the follicular phase, 50+ IU/L during ovulation, and 5-10 IU/L during the luteal phase. Postmenopausal women have much higher levels of 30-200 IU/L.

What does high LH mean?

High LH levels may indicate polycystic ovary syndrome (PCOS), ovarian failure, primary hypogonadism in men, or menopause in women. Elevated levels signal that the pituitary is attempting to stimulate reproductive organs that aren't responding normally.

Why would a doctor order an LH test?

LH tests diagnose fertility problems, evaluate irregular periods, confirm menopause, assess testosterone production, detect pituitary disorders, and evaluate hormone imbalances in both men and women.

What does high LH mean?

High LH levels may indicate PCOS, ovarian failure, menopause, or primary testicular failure depending on the patient's sex and age. It typically means the pituitary is working hard to stimulate reproductive organs that aren't responding normally.

What causes low LH levels?

Low LH can result from pituitary dysfunction, hypothalamic disorders, severe malnutrition, intense exercise, chronic illness, or certain medications. It may indicate the pituitary gland isn't producing adequate hormone to stimulate reproduction.

Can medications affect LH levels?

Yes, hormonal contraceptives, hormone replacement therapy, certain psychiatric medications, and some cancer treatments can significantly affect LH levels and test results.

How is an LH blood test performed?

An LH blood test is a simple blood draw performed at a lab or clinic. The blood sample is analyzed to measure the amount of LH present. Timing of the test may matter for women because LH levels fluctuate during the menstrual cycle.

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Sources

  1. MedlinePlus - LH (Luteinizing Hormone) Test Public Domain
  2. Wikipedia - Luteinizing Hormone CC-BY-SA-3.0
  3. Mayo Clinic - Blood Tests CC-BY-NC-ND-4.0