Definition The luteinizing hormone test is a blood test that measures the amount of luteinizing hormone (LH) produced by the front lobe of the pituitary gland, known as the anterior pituitary.
In men, LH stimulates the production of the male hormone, testosterone. Testosterone is produced by the Leydig cells in the testes.
In women after puberty, menstrual cycles and fertility are regulated by a complex interaction of hormones. These hormone interactions are regulated by the ovaries, pituitary gland and the hypothalamus in the brain.
The hypothalamus produces gonadotropin-releasing hormone (GnRH). This acts as a chemical hormonal signal that stimulates the anterior portion of the pituitary gland. This structure then produces two hormones. These are follicle-stimulating hormone (FSH) and luteinizing hormone (LH).
FSH causes the follicles within the ovaries to mature. The ovaries produce increasing levels of oestrogen as the menstrual cycle progresses. At midcycle, a luteinizing hormone surge occurs that causes a mature follicle in the ovary to release an egg, which is known as ovulation. If the egg is fertilised, a pregnancy will occur.
LH also simulates continued growth of the corpus luteum. This is the remnant of follicle in the ovary that contained the egg. The corpus leuteum continues to produce progesterone. If pregnancy does not occur, the corpus luteum disintegrates. Oestrogen and progesterone levels drop off dramatically.
Who is a candidate for the test? Conditions that may call for LH evaluation in women include:
How is the test performed? A blood sample is taken from a vein on the forearm or hand. First, the skin over the vein is cleaned with an antiseptic. Next, a strong rubber tube, or "tourniquet," is wrapped around the upper arm. This enlarges the veins in the lower arm by restricting blood flow through them. A fine needle is gently inserted into a vein, and the tourniquet is removed. Blood flows from the vein through the needle, and is collected in a syringe or vial. After the needle is withdrawn, the puncture site is covered with a bandage for a short time to prevent bleeding.
What is involved in preparation for the test? There is no preparation for this test. A woman's doctor may request that the test be performed at a certain time in the woman's menstrual cycle. In the case of men and women, recent exposure to a radioisotope during a nuclear medication scan may interfere with test results.
What do the test results mean? Normal values for males are 7 to 24 U/L (units per litre) and for females 6 to 30 U/L.
Greater than normal levels of LH may be found in the following conditions in women:
polycystic ovary disease
premature failure of the ovaries caused by a genetic defect or related to radiation treatment
ovarian cysts, or fluid-filled sacs on the ovaries
the use of oral contraceptives (birth control pills)
Lower than normal levels in men may be seen with:
hypothalamic hypogonadism, or the absence of palpable testes caused by a disorder of the hypothalamus
multiple endocrine neoplasia, or tumours of the endocrine glands
Author: Eva Martin, MD Reviewer: eknowhow Medical Review Panel Editor: Dr John Hearne Last Updated: 21/03/2005 Contributors Potential conflict of interest information for reviewers available on request
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